Can you unequip an inventory bag

1) You can buy or craft more pouches or boxes with various storage sizes and properties (for instance, armorsmiths can craft a 'safe' box that holds 8 items that will not be sorted with compact or moved to collections unless you do so manually).

2) You can also unlock extra pouch/box "slots", via the in-game store.

(At work; can't check the site/wiki to link URLs.)

Unfortunately, there is no way to tell.

You can either keep track manually, or keep killing mobs on your own until it pops.

I've found it helpful to get this achievement over multiple characters; even only two different starting zones should have enough variety to quickly earn the achievement.