What are graham crackers? I can't find them here in the UK, perhaps we call them something different, I did wonder if it's digestive biscuits?? We don't have cool whip either but I expect any type of whipped cream type product would do?
Actually Cool Whip is a "non-dairy whipped topping". I expect most whipped cream products will liquify after a bit, but the non-dairy stuff holds up better. It is usually the item of choice when making many of these desserts, as it mixes well with things like pudding, jello, or cream cheese.