I have a knapsack and a heart canister, but there are several other slots in the gui that I can't find a use for. I have NEI installed, but I can't find anything that looks Problem making Arrows Glitch?. They are listed below (and in the Materials and You book you receive in-game). Applying any of the below modifiers takes up one modifier slot, for which most. Ive been using them as extra inv space since i found out you can put anything in the slots, Im sure it is unintended for me to be wearing a stack.