Fry Thief

If a card says I can steal & eat fries and only one of those is possible what do I do?

Do what you can
Sometimes cards say "Steal 2. Eat 1" or something similar. If you can't perform some of the actions on the card you can still play the card and perform the other actions. So you could for example play a "Steal 2. Eat 1" card and eat a fry on your plate if you opponent has no fries.