According to people who work at grocery stores, these are the things you shouldn't buy. It also depends on how good the store is.

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Pre-packaged cold cuts from the deli. Meaning stuff they sliced up in the store that morning, because they probably used older meat that was about to expire. Even if it was fresh it won't last as long, because the clock starts ticking as soon as they slice it. You're supposed to eat deli meat within three-to-five days.

Bags of pre-shredded cheese. It has additives like wood pulp to keep it from melting. You're better off buying a block of cheese and shredding it yourself.

Pre-made salads at the deli or in the produce section. Sometimes they use old vegetables that are about to expire. Then they add things like olives or hard-boiled eggs so you don't notice that everything else doesn't taste very fresh.

Soup at the deli. Again, a lot of stores save money by using ingredients that are about to go bad. There's no way to tell if it's been sitting out all day. And if it's self-serve, it might be contaminated with bacteria and germs, because dozens of people have probably opened the lid to smell it.

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