Some things which everyone should have and are not that expensive are salt, pepper, spices you like, hot sauce, a soy sauce and Worcester or steak sauce and sugar.
Canned foods are generally safe for a good time after the “best by” date, tho the quality goes down. Other one which are cheap and easy to store are beans and rice. Spam is good to use to flavor the beans and rice.
There was an article in “National Geographic” a few months back saying you can take ordinary clear plastic water bottles filled with water as clean as you can get and place them in bright sunlight for 6 hours and it will kill all bacteria, virus and parasites. It is best to place them on a reflective surface and don’t bother them until the 6 hours are over.
That method of water sanitation is called the SolDis method the water needs to be in a PET container PVC or polycarbonate containers block the UV light that is doing the killing. Also the water has to be clear if it is turbid the UV cannot penetrate deep enough also not more than 3 inches deep again UV cannot get very deep in water even clear water. 6 hours in full sun 2 DAYS in slightly overcast.