Whatever happens when the shit hits the fan it will probably involve fire. In fact fire is a leading cause of death even in normal times.
The cheapest way to prep is to remove flammable materials from your home. Make this an ongoing process.
Give away your books. You are unlikely to read them again.
Get rid of plastic items if you can. Plastic burns but it also emits toxic fumes. Even wood is preferable.
Most fires start in the kitchen. Do not deep fry, this is bad for you as well as a fire risk (and can cause your home to smell like a chip shop).
The most valuable preparations are usually the cheapest.