Plus two for the pillow and plus one for the call of nature kit.
If these have already been mentioned and I missed them apologies:
A map & compass (Even if it isn't really needed, map reading could keep your lad entertained)
Hand sanitizer (Unless you automatically eat with your less favoured hand)
Wet wipes (Easy cleaning)
Spare batteries (For anything you take that needs them)
A small towel (As a rain soaked head, left damp can make even the most grizzled grown man sneezey)
A safety whistles (to signal distress or if out of sight of each other, a much easier and more civilized way to communicate instead of shouting 'Where the F are you?")
Your mobile with you I.C.E contact entered into it and either a spare charged battery or a solar/wind up charger (In case you need to call for help, signal willing)
Camping dogtags on both your persons: you name, age, I.C.E. contact, a list of any medical conditions a first responder would need to be aware of, a list of any medication you take and a list of any medication you may be allergic to (this may seem a bit over the top, but it is one of those 'just in case' things if things do go a bit Pete Tong and if you have some cardboard knocking about, it only takes a couple of minutes to cut round a credit card and write one out)
And finally, a sense of adventure
Welcome to the forum and enjoy your trip
Cheers,
Colin