REI has a pretty good kid's backpack that you can usually pick up used for pretty cheap. That's what each of mine have used until they hit about eleven.
A torso pad or one of the cut down closed cell pads seems to work fine for kids. As long as they're warm, they can sleep on almost anything.
We just run with cheap kid's bags for ours. If it's cooler, I will just tuck the kid in their bag up against me and drape my quilt over them. If it's going to be cold, I bring the wife's quilt along and put it over them in their cheap bag.
My kids get a big kick out of wearing a merino beanie to bed. For some reason, that's a big deal... but it keeps them warm, which keeps them happy.
I agree with what the other guys have said. Snacks are important. Make some trailmix or a combination of nuts as part of your preparations. Binoculars. Maybe use a firestarter rod and some dryer lint to build a fire even if you don't normally. Give him his own headlamp and maybe bring a Luci Light or UV PaqLite. My kids are really into those. And I gotta admit that I really like the UV PaqLites. It's nice to be able to check on them (the kid) without having to turn on a headlamp and fry my eyes.
The only other stuff that I got is to suggest that you make sure that he's drinking enough water and to suggest that you watch closely for when to pull the plug. They get so excited and hum along in high gear all day and then, all of a sudden, they go from full throttle to flame-out. You gotta be able to stuff them in a bag at that point or you're carrying them.