Found a package of ground beef randomly hidden in the very back of the milk cooler. Thankfully kept fairly cool, and still in date, but a customer had stuck it there because he wanted to come back later. He came back the next day and tried to file a complaint because it wasn't there.

Fish left in the bathroom. Like, straight up a pack of salmon fillets, just left there on the top of the toilet tank. Our best guess was that someone wanted to steal it, but either couldn't fit it or got spooked and just abandoned it. It was in a far corner, barely used bathroom, too.

Half eaten fruit or candy thats been shoved to the back of a low shelf. You know a kid did it, there's massive mess back there, and depending on what aisle they hid it in, it might have been there for a couple days to a week. Once found a bell pepper some kid had chomped into.

This is more just "general trash", but still not uncommon if your store has a hotbar: Stolen food containers. People grab their dinner, eat it throughout the store, and then just put the trash wherever. If you're lucky, they leave it somewhere obvious. If you're unlucky, you find an open container of half-eaten rotisserie chicken shoved into a vent after they turned the heat on for the winter. Going past the deli in my store has triggered minor PTSD at times. That smell... Just... Hot rot. That's the only way to describe it. Rotting garbage, oven warmed.