I buy ready chopped onions (white diced and red sliced), peppers and tubes of squeezy garlic. DS is doing food tech this year and keeps asking if we have an onion, garlic clove etc and I have to buy them especially! I buy trays of fresh mash as I really can't be arsed peeling, boiling, mashing and most of all washing it all up afterwards. My kids like cheesy mash, so I stir in some (ready grated) cheese at the end to jazz it up.
People are so snobby about pre-prepared food, but why would I bother slaving over an eye-watering chopping board, peeling and chopping onions, when I can have someone else do it for me and always have them on hand. I used to buy them tinned and ready sauteed too, (Eazee onions I think they were called!) but then Tesco stopped selling them. It was a Delia cheat ingredient. She did a whole book/TV show about it, including frozen mash, but she was a bit patronising about it, and you could tell that she didn't really approve!
I'm all for making my life easier and if that means buying a bag of salad instead of chopping up half a lettuce, then having the other half go brown living in my fridge for a week, so be it.
I also buy pre-chopped mango and pineapple. Mangoes are really difficult to get right, they're either too hard or go brown and the window of opportunity to get them perfect is pretty small, so I buy it cut up so I can see its a nice orange colour. Ditto pineapple, then I also don't have to fill my food waste caddy with a massive pineapple top!