Thank you all for the suggestions! I ended up getting him a stuffed log with squirrels toy while I was at Costco, and that seems to have been pretty helpful since he can pull the squirrels out and I can stuff them back in. I also got him a kong, a nylabone, and an antler from the pet store. So far I've given him the nylabone, and it has also been a hit. (Sometimes I stuff it into the log with the squirrels.)

I'll give him either the antler or the kong once the current crop of toys either get destroyed or lose their appeal.

I like the t-shirt idea - my family always made tug toys with old socks but I currently lack any socks I'm willing to sacrifice. I'll have to see what I have in the way of t-shirts or other similar items. He seems like he would like tug games.

Right now, my biggest issue is that he tends to sleep a lot of the day while I'm working from home, then at night/far too early in the morning it's Dog Party Time!!! which is fun for exactly one of us. I'm working on giving him more reasons to stay awake during the day so he'll hopefully sleep more at night.