Been buying little extra things for yeas. Like a box of matches when I see them at Walmart(housewares near ashtrays and the like). Large containers I wrap in shrink wrap wit hthings liek 25 lb bags of dried beans, sugar. An extra bottle of vinegar to stack back once every couple weeks. As long as you get a little something when you are out at the stores you're doing someitnhg. Walmart is great for things like #10 cans on veggies, 25 lb bags of sugar and the like. We have a store (Save A Lot) that sells things like beans, flour, sugar etc in large containers that can be stored. Just fine one way or another to make sure water stays out. Can fruits and vegetables if you can. When stored properly they will last a LONG TIME. Don't stack jars on top of each other to make sure you don't bust seals. A sturdy box can help there.
It's the little things that will matter. Just pick put a little of this or that. One extra container of...something to put back. Plant a garden and learn to can food. A couple fruit trees come in handy. I want to get into smoking meats but I think I will try and build that. I need to learn more about fermented vegetables. The damn tings last forever (link
Being I have no intention of bugging anywhere as I live in the country as is and have more than one natural water supply, plenty of wooded area for hunting/fuel (springs) I just try to get things I might need should the need pop up
Oh, and keep a decent supply of ammo