My first answer (sort of) is yogurt, but I do need to occasionally buy a small container to use as a starter.
Second is bread. Again, sort of. On very rare occasions, I buy some sort of bread. But it doesn't happen often.
Last: Salad dressings. I simply refuse to spend that much money on something that is so incredibly inexpensive to make. If I'm too lazy to make a proper dressing, I'm happy with a drizzle of vinegar and olive oil.