Adding to the idea of feeding my gang out of a supermarket: I just bought a new Proctor Silex hot pot for $15 from Bed Bath and Beyond. It heats 32 oz. of liquid and we used it to cook pasta, rice pilaf, hard boiled eggs and water for coffee. It's very lightweight. I cooked Shabbat dinner for 4 on Kauai making Costco frozen salmon in a microwave that I kashered out (but I still covered it) and a rice pilaf. Other days of our trip I made pasta, jarred sauce, cottage cheese and microwaved Grillers.
I cheated a little for Shabbat by bringing grape juice boxes and also freezing 2 packages of Costco Meal Mart deli and bringing them in a freezer pouch. Between Walmart and Safeway we found kosher rye bread, bagels, Grillers, cottage cheese, string cheese, two brands of pasta sauce, cream cheese, and the usual cereal, peanut butter and jelly. Walmart had kosher cream of something soup but I wanted to keep my pot parve even though it's blue. Safeway had matzah and grape juice.
Hoping I can find a 220V version of this device!