I would suggest trying to sign up for a summer camp. Preferably one where they are OK with AS kids. I don't think that a generic soccer/baseball/football camp is a great choice, unless Caleb likes those types of things.
What is his hobbies/interests? There are technology camps, art camps, filmmaking camps, all types of camps. But if you live in a small town, you're outta luck mostly. It's the big cities that have the most variety of kids camps.
Maybe take him to a public pool? There's lots of kids that hang out at the parks and pools through the summer. He may make a new friend, or two!
I get those summertime blues quite well. You have loads of friends up through the end of school, and then they scurry away into a million different places. Some in summer sports, some in camps, some playing video games, some on expensive vacations in RVs, some at the beach, some at the library, but it seems like everyone is away from you.
Like I said, try the camps and pool. He may make some good friends.