If you have the energy, try letting him pick a topic and run with it.
My kinder heard about some homeschoolers who made an ancient Egyptian lunch and now is begging me to homeschool 'at least on Saturdays' because 'otherwise I won't get to learn ANYTHING until like THIRD GRADE!!!' (tears and tantrums). She wants to study frogs that freeze solid in the winter, and she will probably branch out into other hibernation strategies. She also wants to engineer solutions to everything, so she gets lots of time with the recycling bin and a roll of tape. This particular kid would benefit from a robotics team, possibly a Destination Imagination team, and a theater club.
My older one was different. We had unusual math puzzle workbooks around that she loved, signed up for EPGY open enrollment online math, and spent lots of time in the kids' nonfiction section at the library. Teams and competitions would have been torture for her. She liked setting up science experiments, but didn't have the engineering drive I see in her sister.
Which is a very long way of saying follow the child. Notice what makes his interest spark and do lots of that. Don't withhold any advanced learning he craves, but your main job at this age (any age?) is to keep him engaged, interested, and hopeful that learning does not equal drudgery.