It is no problem, if you don’t have as many varieties of cheese, double up on what you do have. Cheddar, American, Colby are all great options for a good melt. You can also use Parmesan as topping if you have. But the authentic Dinosaur BBQ Mac and Cheese use all the cheeses listed above, so if you are looking for that flavor, you’ll have to use all the different kinds of cheese. It is perfectly fine to use slices of cheese if that is what you have, as all the cheese gets melted anyway.