I have had different cats eat things as diverse as:
rice with butter and soy sauce
mushrooms off the pizza, but left the cheese
a take-out taco stolen from the bag when we weren't looking
soggy cereal out of a bowl of milk, but left the milk
I don't actually set out to feed them this stuff. With a small child, we sometimes leave food on the table and they get up there. Also, hubby likes to eat in bed (yuck) and there is often a plate of crumbs on the floor next to him. The onion rings and mushrooms were accidental. The cat in question was begging - as much as they ever "beg" - and out of annoyance I finally held a piece out saying, "Here you go, you silly beast, you won't even like it!" only to watch it disappear down a furry gullet with a purr. And of course it was followed up with more persistent "begging"!
And of course these are food items. I assume that most cats eat for their bodies' needs so a periodic serving of salsa meets some nutritional need. I have a friend whose cat eats soap and leather shoes (like the fringe off loafers), and I think that is a health problem. A little broccoli now and then seems pretty safe.