Food is an artifact type. Even though it appears on some creatures, it's never a creature type.

You can't sacrifice a Food to pay multiple costs. For example, you can't sacrifice a Food token to activate its own ability and also to activate Maraleaf Rider's ability.

Whatever you do, don't eat the delicious cards.

Bartered Cow's ability is a triggered ability, not an activated ability. It doesn't allow you to discard it or sacrifice it whenever you want; rather, you need some other way of discarding it or causing it to die.