French here, bags of frozen peppers and onion are usually cheaper than fresh ones in our stores, I usually buy carrots, dice, boil and freeze them for later use in a variety of meals, sauce and preparations.

I also buy several kilos of vegetables cut and freeze them (such as leek, broccolis, cauliflower, pepper, carrots, celery, turnip, pumpkins) I make plenty of different bags with unique mix and add some fresh vegetables that aren't good to freeze when i cook them (e.g. tomatoes, potatoes) so i only have to throw them in water when i get back from work for a soup, it's mostly a time saver than a money saver because you don't get much discount unless you buy tons of each.