Honestly the whole ice cream depends on my mood it's easy to pick up ice cream to take home and have in privacy.
That being said I do enjoy the variety of cool flavors at ice cream shops and it can be fun to lick the ice cream off cone.
I'd probably go for at home unless I really wanted a certain flavor or was in the mood to get it from shop.
Drive in as in go into a restaurant? Obviously drive thru is easy but for me, a lunch treat, is going in and sitting down somewhere, taking a little time out of the day to try to relax a bit and enjoy watching people bustle by while I pretend I'm some elegant lady that has all the time in the world (even if it's not totally true, lunch hours don't last forever)
Go to a summer festival win a live gold fish or Go to a summer nature retreat, where you do a bunch of nature activities (hikes, camping etc) but with a group of people ?