These are the only stickers you will ever need! They are officially licensed by Cephalofair(Gloomhaven creator) and are removable, so play Gloomhaven over and over again until you can recite every scenario from memory! Seriously, don’t go anywhere else, these are the best. Here is the link to the exact ones I have.
These are a nice cheap solution to organize all of your monsters. This is what I am currently using myself! Here is the link to them. Don’t wait!
The best organizer I have seen. Expensive but definitely worth it. Check out the link here and stop putting all of your stuff in ziploc bags and envelopes!