You mean, in addition to what you are already getting? For example, say you are getting the cheeseburger meal at Pecos Bills. That already includes fries OR carrots, plus drink and dessert. If you wanted ANOTHER order of fries, you could use a snack credit for that, but not free.
We did this at Flame Tree- we got our rib meals, and then were going to pay out of pocket for the onion rings- the cashier said, "You can use a snack credit for those if you want." We said, "Heck ya!"