We have used Costco several times, (as a matter of fact I believe I have the honor of being the one that discovered this and first posted it on the board a couple of years ago!) they do have some snack items you can order like cheese-peanut butter crackers, granola bars, flavored coffee creamer, etc. Not a whole lot to choose from, but all of it is cheaper than buying it as individual items from Disney.
I also wonder how much longer they will keep doing the water shipments as I can't see how they're making any profit at all. In the beginning I thought they might have a distribution center close by and could deliver it locally -- but it came via UPS, so I can only assume they've got some kind of bulk shipping rates that make it possible. So in other words, take advantage of this service while you can!!!