Rapacious Guest's third ability triggers whenever you sacrifice a Food for any reason, not just to activate a Food's activated ability.

To determine the amount of life the target opponent loses from Rapacious Guest's last ability, use Rapacious Guest's power as it last existed on the battlefield, not its power in the graveyard.

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.

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

If an effect refers to a Food, it means any Food artifact, not just a Food artifact token. For example, you can sacrifice Tough Cookie (an Artifact Creature — Food Golem) to activate Maraleaf Rider's ability (an ability with "Sacrifice a Food" in its cost).

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