kick off walls
you can kick off of objects to gain backwards momentum

grab enemies
holding left click on someone while unarmed will grab them

kick grenades
kicking a grenade as you throw it sends them farther

grab props
holding g on some props will grab them

disarm enemies
punching someone in the gun will give it to you

holster weapons
pressing 1 and 2 lets you store the weapons you have in your hands