I never knew about stuff like this until yesterday, but apparently some food items are available online, in bulk, at prices FAR below what you pay in grocery stores.
Personally, I'm a big fan of "tinned fish". I love sardines, tuna, mackerel, and herring. My favorite is the "kippered" herring, the smoked kind. I'm a big fan of the "Polar" brand, it makes a great quick meal with some crackers, cheese, pickled veg, and a beer.
The tins cost about $3.50 in my local supermarket. Check this out, I can get a package of 18 from Amazon for only $21.50! That's like $1.19 per tin! These are TOP QUALITY German-canned kippers, definitely at the premium end for this kind of product in America, but I'd be getting them for peanuts.
18 Pack Case of 3.54oz. Kipper Snacks: Amazon.com: Grocery
Not sure what other food items can be bought this way, but I'll definitely be on the lookout.