This disposable fiberboard container folds flat and has a bladder that can hold a gallon of gas (about 14″ by 6″ by 2″). I’ve yet to have a car emergency, but I’ve used it for a prosaic fill up on a lawn mower. No leaks, easy to carry and cheap to replace. Keeping one around is handy and comforting, and it’s way better than the bulky plastic ones that have bounced around in the back of my car for years.
Gas-O-Haul (now Itzagascan)
Available from DSK Sales
[Note: The Gas-O-Haul has been renamed and is now Itzagascan. In addition, it is no longer legal in several states including NH, NY, IL, TX, IA, OR, DE, and MA. --OH]