I think just hanging out with them is very underrated!
Other than that, there's plenty to keep yourselves mentally & physically exercised. Take him for walks, teach him to 'dance' with you, play 'chasey', teach some tricks - I agree, soccer is fun! Set up an obstacle course, teach him some of that other stuff that you always meant to but haven't got around to, improve things you've already taught him...
Yep...perfect time for bombproofing..get out all those really scary things like blowing tarps, styrofoam cups rolling around, your arms waving around, oh and those really scary things that eat horses...plastic bags. :)
I don’t ride my horse that much, but I do a lot of “long rein” training, and we both have great fun with that J You can do all kinds of stuff then, go for a walk, do dressage, train him to pull stuff. It’s a fun way to teach your horse new movements that you can use when you ride. And as a bonus you get some exercise too.