I suppose a lot of it has to do with what he knows how to do. For example, what do you intend for him to do with the paracord? It's useful stuff, but I wouldn't expect him to be able to build a shelter or rappel down a cliff in an emergency at his age. I'd say extra food would be a higher priority. Tell him not to snack on his emergency rations (vbg).

Ditto the saw and the firesteel. He can break small stuff with his hands and feet, so he doesn't really need the saw. And a Bic lighter is easier for anyone to start a fire with. Your idea of adding tinder is a good one.

I'd add spare batteries for the flashlight. Make sure he wears a hat with a brim. Also, depending on the weather you may want to add a small tube of sunscreen. I'd think he's old enough to learn not to eat the Micropur tabs. Other than that they're safe. After all, you're supposed to drink them. He can probably also understand about the nasty bugs in the water.

I've never really carried a towel hiking. I do carry a bandana, though. You might save some space by substituting.

If there's any spare room, an extra pair of socks are very, very important.

Sounds like a great trip. You guys have fun.

Kevin B.