Along with cash, as has been mentioned, consider an extra supply of things your neighbors will run out of (TP and tampons always make good tender) that you can trade. It buys good will and friendship, as well as another pair of eyes on your property, both while you're home and away. If there are people you trust in your building, consider forming a coop, both for sharing and security.
As far as food goes, a lot of good suggestions already. Consider getting a dehydrator. They're cheap and don't take up a lot of space. You can dehydrate meats, fruits, veggies and all kinds of other stuff, and reconstitute them for meals or eat them like jerky and trail mix. They also travel well if you have to bug out or run out for supplies.