First thoughts:

The MXZ saw has received less than wonderful reviews, particularly in wood. If you're going to give him a saw, let him have a real one, not one that makes adults cry and stomp and say naughty words. (Or in the case of my brother, take it to the firing range for summery execution.)

He's eight? Does he know how to safely start a fire? Learning that should be rewarded with the firesteel. Red poncho + whistle + heat pack should get him found fast enough.

Water tablets and little kids... Not knowing him, I'll err on the side of caution and say that this is one of the few times were one of the filter straws might come in handy. Or better, set him up with one of the bottles with the filter built into it.

And from the way you said it, the whistle is probably special to him. So I'm going to reluctantly go into ogre mode, and say that he should have something pealess.

If you have the time and the green, the mylar sheet upgrades well to a Heatsheet. Normally I'd recommend the bivy version, but it doesn't breath so well if he curls up at the bottom of it.

A family picture, with names, address and telephone number on the back of it.

Also, do you know how the buttpack rides on him? Does it feel comfortable, and not migrate to his ankles? A small day pack might be better.