Duplicate Item:

First you tell someone to host then you join and make it so all items come in the invetory (If you don't wanna lose them all). Then you find a enemy who can kill you (or your friend). Then when it says press Space do not do it! Go out from it and join it again and all of your stuff will be there on the ground (all you had in your inventory) plus you still have the stuff before you died.