Old Flitterfang's triggered ability will check as the end step starts to see if a creature died this turn. If none did, the ability won't trigger at all.

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.

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