In case you skip tutorials, here's a screenshot.

Eren
Favorite – Perfect Replica Blades.
Really Likes – Anti-Titan Manual Part 2.
Likes – Titan Training Dummy, Anti-Titan Manual Part 1, Where Mom Lives, Thick Parka and Training Equipment.

Mikasa
Favorite – Training Equipment.
Really Likes – Anti-Titan Manual Part 2, Perfect Replica Blades and Titan Training Dummy
Likes – Anti-Titan Manual Part 1, Weapons Engineering Lecture, Emergency Kit, Rose Bouquet, Elegant Bedding and Leather Gloves.

Armin
Favorite – History Of The Walls.
Really Likes – Interior Sightseeing Map and Chess Set,
Likes – Weapons Engineering Lecture, Quill Pen, Sketch Book, Elegant Bedding, Emergency Kit and Thick Parka.

Reiner
Favorite – Soldier’s Handbook.
Really Likes – Leather Gloves and Titan Doll.
Likes – Anti-Titan Manual 1, Anti-Titan Manual 2, Interior Sightseeing map, Pomade, Elegant Bedding, Silver Ring, Golden Necklace, Thick Parka, Titan Training Dummy, Training Equipment, Special Newspaper and Regiment Medal.

Bertholdt
Favorite – Elegant Bedding.
Really Likes – Titan Doll.
Likes – Anti-Titan Manual 1, Anti-Titan Manual 2, Soldier’s Handbook, Interior Sightseeing Map, Hungry Titan, Strange Vase, Strange Painting, Dust Rag, Ultimate Dust Rag, Gold Bar, Titan Training Dummy, Training Equipment, Regiment Medal, and Strange Fossil.

Annie
Favorite – Thick Parka.
Really Likes – Leather Gloves, Training Equipment and Titan Doll.
Likes – Black Tea, Anti-Titan Manual 1 and 2, Where Mom Lives, Gold Bar, Rose Bouquet, Silver Ring, Titan Training Dummy and Perfect Replica Blade.

Jean
Favorite – Rice Omelett
Really Likes – Where Mom Lives.
Likes – Weapon Engineering Lecture, Interior Sightseeing Map, Hungry Titan, Pomade, Gold Bar, Chess Set, Silver Ring, Golden Necklace, Thick Parka, Leather Gloves and Perfect Replica Blades.

Conny
Favorite – Where Mom Lives.
Really Likes – Hungry Titan.
Likes – Anti-Titan Manual 1 and 2, Interior Sightseeing Map, Gold Bars, Elegant Bedding, Thick Parka and Perfect Replica Blades.

Sasha
Favorite – Hunter's Armory, Marbled Meat.
Likes – Field Provisions, Stale Bread, Black Tea, Anti-Titan Manual 1 and 2, Interior Sightseeing Map, Hungry Titan, Where Mom Lives, Elegant Bedding, Thick Parka, Emergency Kit, Perfect Replica Blades and Regiment Medal.

Christa
Favorite – Horse Brush.
Really Likes – Rose Bouquet and Emergency Kit.
Likes – Stale Bread, Black Tea, Anti-Titan Manual 1 and 2, History Of The Walls, Interior Sightseeing Map, Where Mom Lives, Quill Pen, Sketchbook, Silver Ring and Special Newspaper.

Ymir
Favorite – Hair Tie.
Really Likes – Gold Bar and Titan Doll.
Likes – Black Tea, Interior Sightseeing Map, Hungry Titan, Silver Ring, Golden Necklace, Gem Stone, Leather Gloves and Special Newspaper.

Levi
Favorite – Ultimate Dust Rag and High Quality Tea.
Really Likes – Silver Ring and Perfect Replica Blades.
Likes – Black Tea, Cheap Alcohol, Anti-Titan Manual 1 and 2, Dust Rag, Training Dummy and Training Equipment, Leather Gloves and Special Newspaper.

Hange
Favorite – Strange Fossil.
Really Likes – Anti-Titan Manual 1 and 2, Weapons Engineering Lecture, Quill Pen, Sketch Book and Titan Doll.
Likes – History Of The Walls, Hungry Titan, Where Mom Lives, Chess Set, Elegant Bedding, Emergency Equipment, Hair tie, Perfect Replica Blades and Special Newspaper.

Erwin
Really Likes – Perfect Replica Blades
Likes – Anti-Titan Manual 1 and 2, Soldier’s Handbook, History Of The Walls, Weapons Lecture, Quill Pen, Chess Set, Pomade, Silver Ring, Leather Gloves, Titan Training Dummy, Training Equipment, Emergency Kit and Regiment Medal.

Marco
Likes – Dried Meat, Marbled Meat, Rice Omelet, Stale Bread, Soldier’s Handbook, History Of The Walls, Weapons Engineer Lecture, Quill Pen, Sketch Book, Pomade, Gold Bar, Chess Set and Strange Fossil.

Thomas
Likes – Stale Bread, Soldier’s Handbook, Interior Sightseeing Map, Pomade, Gold Bar, Elegant Bedding, Thick Parka, Titan Training Dummy, and Training Equipment.

Mina
Really Likes – Rose Bouquet.
Likes – Stale Bread, Black Tea, Soldier’s Handbook, Interior Sightseeing Map, Gold Bar, Elegant Bedding, Thick Parka, Titan Training Dummy, Training Equipment and Emergency Kit.

Miche
Favorite - Soothing Herb.
Really Likes – Perfect Replica Blade.
Likes – Black Tea, Anti-Titan Manual 1 and 2, Soldier’s Handbook, Pomade, Leather Gloves, Titan Training Dummy, Training Equipment and Special Newspaper,

Ouro
Really Likes – Ultimate Dust Rag and Regiment Medal.
Likes – Black Tea, Cheap Alcohol, Anti-Titan Manual 1 and 2, Where Mom Lives, Dust Rag, Gold Bar, Pomade, Elegant Bedding, Golden Necklace, Titan Training Dummy, Training Equipment and Perfect Replica Blade.

Petra
Really Likes – Where Mom Lives, Ultimate Dust Rag and Rose Bouquet.
Likes – Black Tea, Anti-Titan Manual 1 and 2, Soldier’s Handbook, History Of The Walls, Weapons Engineering Lecture, Interior Sightseeing Map, Quill Pen, Sketchbook, Dust Rag, Gold Bar, Elegant Bedding, Silver Ring, Titan Training Dummy, Training Equipment, Emergency Equipment, Perfect Replica Blade, Special Newspaper and Regiment Medal.

Gunther
Really Likes – Ultimate Dust Rag
Likes – Black Tea, Cheap Alcohol, Anti-Titan Manual 1 and 2, Soldier’s Handbook, Dust Rag, Pomade, Gold Bar, Elegant Bedding, Golden Necklace, Titan Training Dummy, Training Equipment, Perfect Replica Blade, Special Newspaper and Regiment Medal.

Eld
Really Likes – Ultimate Dust Rag
Likes – Cheap Alcohol, Anti-Titan Manual 1 and 2, Soldier’s Handbook, Weapon Engineering Lecture, Quill Pen, Sketchbook, Dust Rag, Pomade, Gold Bar, Chess Piece, Elegant Bedding, Silver Ring, Golden Necklace, Titan Training Dummy, Training Equipment, Perfect Replica Blade, Special Newspaper and Regiment Medal.

Moblit
Really Likes – Sketchbook
Likes – Cheap Alcohol, Soldier’s Handbook, Where Mom Lives, Quill Pen, Pomade, Gold Bar, Elegant Bedding, Special Newspaper, and Regiment Medal.

Ian
Likes – Cheap Alcohol, Soldier’s Handbook, Pomade, Gold Bar, Leather Gloves, Training Equipment and Regiment Medal.

Rico
Likes – Black Tea, Soldier’s Handbook, History Of The Walls, Weapons Engineering Lecture, Where Mom Lives, Chess Set, Rose Bouquet, Silver Ring, Emergency Kit, Regiment Medal,

Mitabi
Likes – Cheap Alcohol, Soldier’s Handbook, Pomade, Gold Bar, Leather Gloves, Training Equipment and Regiment Medal.

Nile
Loves – Iron Bamboo Kit.
Really Likes – Soldier’s Handbook.
Likes – Cheap Alcohol, History Of The Walls, Where Mom Lives, Pomade, Chess Set, Leather Gloves and Regiment Medal.

Marlo
Really Likes – Soldier’s Handbook.
Likes – Stale Bread, History Of The Walls, Pomade, Chess Set, Thick Parka, Emergency Kit and Regiment Medal.

Hitch
Really Likes – Gold Bar and Rose Bouquet
Likes – Stale Bread, Black Tea, Interior Sightseeing Map, Hungry Titan, Where Mom Lives, Golden Necklace, Gemstone and Thick Parka.

Hannes
Favorite – Pricey Alcohol (didn't confirm).
Really Likes – Cheap Alcohol.
Likes – Weapon Engineering Lecture, Interior Sightseeing Map, Where Mom Lives, Pomade, Elegant Bedding, Golden Necklace and Training Equipment.

Pyxis
Favorite – Chess Set, Pricey Alcohol
Really Likes – Cheap Alcohol
Likes – History Of The Walls, Weapon Engineering Lecture, Interior Sightseeing Map, Strange Vase, Strange Painting, Strange Object d’Art, Quill Pen, Sketchbook and Elegant Bedding.

Keith
Favorite – Titan Training Dummy.
Really Likes – Training Equipment.
Likes – Anti-Titan Manual 1 and 2, Soldier’s Handbook, Leather Gloves, Perfect Replica Blade and Special Newspaper.

Kitz
Favorite – Soothing Herb.
Really Likes – Quill Pen, Sketchbook.
Likes – Cheap Alcohol, Soldier’s Handbook, Weapon Engineering Lecture, Pomade and Elegant Bedding.

Zachary
Favorite – Strange Objet d’art
Really Likes – Strange Painting and Regiment Medal.
Likes – Cheap Alcohol, Soldier’s Handbook, Weapon Engineering Lecture, Strange Vase, Quill Pen, Sketchbook, Pomade, Chess Set, Elegant Bedding and Special Newspaper.

Nanaba
Really Likes – Perfect Replica Blade.
Likes – Black Tea, Anti-Titan Manual 1 and 2, Soldier’s Handbook, History Of The Walls, Weapons Engineering Lecture, Where Mom Lives, Chess Set, Rose Bouquet, Leather Gloves, Titan Training Dummy, Training Equipment and Sp

Daz
Really Likes – Soothing Herb.
Likes – Stale Bread, Interior Sightseeing Map, Hungry Titan, Where Mom Lives, Pomade, Gold Bar, Elegant Bedding and Emergency Kit.

Nick
Favorite – Gemstone
Really Likes – History Of The Walls
Likes – Black Tea, Where Mom Lives, Strange Vase, Strange Painting, Strange Objet d’Art, Quill Pen, Sketchbook, Pomade, Gold Bar, Elegant Bedding, Silver Ring and Golden Necklace.

Merchant Boss
Favorite – Golden Bar.
Really Likes – Golden Necklace, Weird Fossil and Gemstone.
Likes – Weapons Engineering Lecture, Interior Sightseeing Map, Hungry Titan, Where Mom Lives, Strange Vase, Strange Painting, Strange Objet D’art, Quill Pen, Sketchbook, Pomade, Elegant Bedding, Silver Ring and Leather Gloves.

Gelgar
Really Likes – Cheap Alcohol, Pricey Alcohol, Pomade, Perfect Replica Blade
Likes – Anti-Titan Manual 1 and 2, Hungry Titan, Where Mom Lives, Elegant Bedding, Silver Ring, Leather Gloves, Titan Training Dummy, Training Equipment and Special Newspaper.

...honestly, it's just a really late addendum.

Regiment store gift shop
Assorted field provisions (1000), Stale bread (1200), Black tea (1500), Cheap alcohol (1800), Titan training dummy (5200).
One of the first gift shops you get to visit. The only thing to note is that Titan training dummy is not sold there from the beginning.


Central plaza gift shop
Anti-Titan manual part 1 (2000), Soldier's handbook (3000), Interior sightseeing map (3000), Hungry Titan (3000), Quill pen (1800), Sketchbook (2500).
Can be seen on the map.

Large store gift shop
Silver ring (2100), Golden necklace (3100), Hair tie (4200), Thick parka (4600), Leather gloves (2700), Camouflage uniform (3900).
Usually Merchant Association Boss loiters nearby or inside of it.

Back alley shop
Dust rag (2000), Ultimate dust rag (4500), Pomade (2800), Training equipment (6400), Emergency kit (1900).
The store is close to Order of the Wall facilities, where Nick is usually stationed.


Central plaza north gift shop
Gold Bar (10000), Chess Set (4200), Rose Bouquet (4000), Elegant Bedding (5800), Gemstone (6500).

Central plaza south gift shop
Anti-Titan Manual Part 2 (6000), History of the Walls (3000), Weapons Engineering Lecture (3000), Where Mom Lives (3000), Strange Vase (2300), Strange Painting (3500), Strange Objet d'Art (4600).

Store gift shop
Fresh Bread (2000), Marbled Meat (8000), Rice Omelett (2600), High Quality Tea (3500), Pricey Alcohol (4000), Water of the far north (1600).

To get access to this location, you must become friends with Sasha. It unlocks at friendship rank 5 with her. This location also sells best horses (as far as I know, at least).

Farming village gift shop
Dried Meat (3000), Hunter's Armory (2700), Horse Brush (2000), Soothing Herb (3000), Iron Bamboo Kit (3500).

Perfected Replica Blade (6000), Special Newspaper (6000), Regiment Medal (6000), Strange Fossil (6000), Titan Doll (12000)

Maybe later I would be arsed to make this guide more detailed (like showing what shops sell which gifts and how to get access to them), but for now this will do.
Guide is incomplete, so any feedback is welcome.