Keep it on the shelf - lasts basically forever

1. Olive oil - You can basically use this for whatever you want, despite what people might say. Get the big 4L cans if you can. Mine last about a year.
   
2. Vinegar - You should have at least two or three kinds, but you can get small bottles, they'll only cost a couple bucks. Some good and basic choices are balsamic, white, red wine. But they keep, so if you see something interesting, even if you're not sure if you'll ever use it, just pick it up. You won't regret it.
   
3. Stock- Bouillon cubes or cans or boxes. I'd say go whole hog and get chicken, beef and veggie.