Hunger vs cravings
Good question. First, you know how long it has been since you last ate and what your body's needs are.
Use that to assess whether a craving makes sense. Second, remember that many cravings are not really hunger, but thirst. Drink some water first and wait. This will take care of a lot of cravings. Third, analyze what you're craving--if it's a cookie or a twinkie, you're not really hungry.