Ice cream sandwiches and cake are summer classic, they're very practical because you can prepare them ahead of time and keep the frozen. You could even create a bar with different types of cookies and ice creams so everyone can make their own.
These are my daughters' favorites since they love peanut butter and jelly. I use ready to bake peanut butter cookies and strawberry ice cream. Then I dip them in chocolate and sprinkle them with chopped peanuts. Delicious!