[Endoperez]

I'm not sure if supply items increase supplies or reduce the amount of supplies your units need. It could be either way.

The supply items work some way or other, and stack with each other, but identical items wielded by the same commander don't stack. That is, Summer Sword, Cauldron of Broth and Endless Bag of Vine all stack together, but two Cauldron's on the same commander won't. You can have ten commanders with the sword, bag and cauldron, though, and the commanders' effects stack.