How can I ask a guy I've known for a while out casually?

I’ve known this guy since I was little. Lately, we’ve have a lot of classes together, and I’ve developed a huge crush on him (to the point that just thinking about asking him out makes my heart pound), and I wanted to ask him out. Casually. Of course, when I talk to him, I have no problem, and it’s not awkward, because we’ve known each other for so long. Any ideas?
(I’m going to rule out asking him to a movie, restaraunt, or anything fancy, or very secluded)

Thanks for any help :)