Rat? This is a ratburger?
The cheese does not necessary need to come from a cow, and neither does the meat. Meat can be ground up from just about anything...squirrel or opossum if necessary. Any green edible leaf will do in place of the lettuce. Catsup, pickels, and mustard keep for a very long time. Fresh tomatoes are not required, they make the burger better but are not mandatory. Onions keep for quite awhile but can be canned or dried, and for that matter so can the tomatoes.
Rat? This is a ratburger?