There are 4 collection-type achievements in Octopath Traveler:

All of them are quite difficult to achieve because there isn't an index of collections in the game to let you know your progress. Therefore it's highly recommended to use this spreadsheet for auxiliary:
https://steamproxy.net/sharedfiles/filedetails/?id=2309451625
This spreadsheet is composed by @marcv666 and translated into other languages by many players. Many thanks for their excellent work!

Besides, you have to pay attention that there are some missable items/chests/weaknesses in the game. Once you miss them you could only accomplish the achievements by creating a new save data, which is painful. Therefore I also recommend you to refer to this guide:
https://steamproxy.net/sharedfiles/filedetails/?id=1796269606
However, you might still get into trouble even if you've obtained each missable item and checked each checkbox in the spreadsheet. Because that's quite a long journey to finish these achievements. it's normal to make some mistakes during completing the checkboxes. For instance, there are 734 necessary chests and many players finally found that they completed the spreadsheet but didn't get the [Treasure Hunter], including me. It's disappointing and annoying to re-check each item, but that's the only solution. If you unfortunately bump into the same situation, this guide is for you.

In this guide, I'd like to introduce a remedy scheme through savefile-checking. It's achieved by save editor and you could download it from this link[github.com]. In advance, I declaim that:

From my perspective, I would not recommend directly modifying the save data, which might affect the game experience.
But only checking the save file can be a good solution to save a lot of unnecessary time overhead and improve the experience.

Moreover, this method is mainly for the [Strategist], [Treasure Hunter], and [Eagle-Eyed]. It may not suitable for the [Collector]. But the [Collector] would be easier than others because you can check each item's amount in your bag and compared them to the spreadsheet conveniently.

At last, Special thanks to @SUDALV and @Tele3000. @SUDALV adds functionalities in the save editor, enabling it for checking the weaknesses and treasure states. @Tele3000 creates a Google doc for associating each monster's savefileID and its name, greatly facilitating the weakness checking. @foxid finds out the relationship between each location's ID and its name. He validates and completes the Google doc for treasure state. I do the basic work for the treasure state doc. Also I beautify it based on @foxid's work and verify some details.

Firstly you could download the save editor from this link[github.com].
Unzip the compressed file and you can run the OctopathTraveler.exe.

The save files should be in this directory:

C:\Users\(User name)\Documents\My Games\Octopath_Traveler\(ID)\SaveGames

The SaveData0.sav corresponds to the automatic save, while SaveData1\2\3.sav refers to the corresponding sequence of manual save data. These .sav files can be loaded by the save editor.

Click the folder icon, or select (F)ile -> (O)pen from the menu.
Afterward, we mainly focus on the "weak" tab and "TreasureState" tab.

This chapter is for Strategist.

In the "weak" tab, you can see the list of monster's ID and its weaknesses:
You can check your missed weakness as follows:

1. Open your save file as aforementioned.
   
2. Turn to the "weak" tab.
   
3. Open the MONSTERS ID LIST[docs.google.com]
   
4. Compare your save file to the google doc.

You could mainly focus on columns A, C~O, and Q for comparison.

This chapter is for Treasure Hunter and Eagle-Eyed.

In the "TreasureStates" tab, you can see the list of location's ID and its states:

You can check your missed chests/hidden items as follows:

1. Open your save file as aforementioned.
   
2. Turn to the "TreasureStates" tab.
   
3. Open the LOCATION ID LIST[docs.google.com]
   
4. Compare your save file to the google doc.

Description of Location ID List:

• Column A is the location ID that corresponds to your save data.
  
• Column E is the location's name.
  
• Column B is the sum of all treasure chests and hidden items in a location.
  
• Column C&D is the sum of chests and hidden items respectively. It's verified that the data structure of the state should be [Chest + Item]
  
• Column G is some tips indicating the missable hidden items.

Example:
According to the Location ID List, the "1257303" is "Cobbleston". Its summation is 7, which means your treasure state is expected to be “1111111”, where the first 2 are for chests and the last 5 are for hidden items.
If your treasure state of there is “1011111”, you've missed a chest.
If your treasure state of there is “111111”, you've missed a hidden item.

@Tele3000 makes the list by checking each monster manually. Many thanks to his fantastic work!
Some monsters are matched by tameID, the weakness occurrence, and clustering. Besides, there may be a dozen monsters that are swapped. The ones that could be swapped are monsters with the exact same weakness binaries. Therefore welcome for the reports!

There is also another monster ID list crafted manually by github user @BeyondTheHorizon. You can download it from here[github.com] and use it as alternative reference.

There is no information about the location ID and its name. Thus I have to sum up every "1" in each location's state at first and build the basic version of the Location ID List.

Afterward, @foxid finds out the relationship between each location's ID and its name. He finds that IDs of the locations in the same area ( e.g., the Flatlands ) are continuous and in order. He also discovers the structure of the state should be [chest + item], and finally matches most of the locations. Many thanks to his prominent work!

Lastly, we validate some locations that have the same treasures. If you find some mistakes, you are welcome to contact me at any time to supplement~