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.

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

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.