What would be a good item to have a stock of that one could use for barter?
My thought is don't purchase stuff specifically for bartering. You'd be better off buying extra of stuff you know you'd use (cans of tuna, wool socks, batteries, first aid supplies, shoe laces, etc...). That would be the most effcient use of your money and storage space.
There've been some good bartering threads here. Do a search and you'll find them.
-Blast