If the target creature is an illegal target by the time Insatiable Appetite tries to resolve, the spell won't resolve. You won't sacrifice a Food.

You choose a target creature as you cast Insatiable Appetite, but you don't choose whether to sacrifice a Food until the spell resolves.

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).