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).

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.

Elanor Gardner doesn't need to have been on the battlefield when you sacrificed a Food this turn. For example, if you sacrifice a Food during your first main phase and you cast Elanor Gardner during your second main phase, its last ability will trigger at the beginning of your end step.

Elanor Gardner's last ability will trigger only once during your end step, no matter how many Foods you sacrificed this turn. However, if you haven't sacrificed any Foods this turn as your end step begins, the ability won't trigger at all. It's not possible to sacrifice a Food during the end step in time to have the ability trigger.