This method is the cleanest way I've found to have plenty of burger patties on hand. They aren't as good as freshly grilled, but if you've got to just grab something nourishing, these will do the trick. You can take them on the plane as long as your bag isn't over 4 ounces. Cut them into "fries" for easy eating.
Preheat oven to 250 degrees.
Place frozen hamburger patties on a cookie sheet covered with heavy duty foil. Season generously with salt.
Cook for 20 minutes. Flip patties and season with salt again.
Cook for another 20 minutes. They are done at 165 degrees, but I usually stop at 155 degrees.
Remove patties to a plate to cool, then refrigerate.
This method will work for patties that are not frozen. You'll just need to shorten the cooking time.
Clean-up should just be to let the cookie sheet cool and then throw away the foil. If you want to make tallow, pour the grease into a jar while it is still hot.