What you can do with the potato chips (crisps) likely depends on how they've been cooked and how heavily seasoned they are. You'll likely want to leave out any salt from later recipes that you might try to make.
My first thought is much in line with your idea of a casserole, as I would be to try to make a potato kugel. The difference in available starch might give it a less than ideal texture, but if it works, it'd be a way to use up a lot of potatoes quickly.
My second thought would be to make something similar to a tortilla de patatas. You typically fry the potatos first, and then add the hot potatoes to beaten egg so it'll temper slightly, then pour the mix into a pan to cook ... which means cold potatoes might not work. Instead, we might look to a similar italian dish that uses leftovers (although it's leftover pasta, not potatoes). It goes by the name of Pizza di Spaghetti or Frittata di Spaghetti; you heat the leftovers in your pan, then pour an egg mixture over top. You may have to chop the chips up so the eggs can trickle through the potatoes. You either cook and flip, or slide the whole pan into the oven to let it set.
As you can add just about anything to fritatas, if you have a lot of potatoes to use up, it's nice that you can saute up other vegetables to add, or cooked meat (sausage or ham would be traditional, but might bring too much salt; you'll have to experiment)