My players were recently using caltrops to trap doorways in a dungeon, and it became difficult to keep track of where things were trapped. These 25mm tiles hold 20 caltrops (ie a full bag which is needed to cover a 5'x5' square).

I find that my players having interact-able props really helps get them into the story. I hope it does the same for yours.

UPDATE: April 7, 2018
I ran the model through Meshmixer and added the v2 model. The file is a little larger, but it should print easier.