I use two ice chest. In one of them, I have all my stuff, with some ice to keep it cold. In the other one, I load just dry ice, and open it once a day only to refresh the first one. It also helps if you seal it with tape to make sure there's no leaks. It's worked while camping for one week out in the desert with 100+ degree temperatures, but it's a little bulky. For a long term roadtrip, I'd just keep buying ice at gas stations an supermarkets. You can find it almost everywhere for only a couple of dollars.