I think the kit looks good, and I'd agree with the advice I've seen so far.

My first suggestion would be to find out what you can about the Hug-a-Tree program. Hug-a-Tree page
They've been working on updating their program for more than a year now, and to the best of my knowledge, they don't yet have the new version up and running, but the basics are very simple to acquaint yourself with. Google searches will come up with other sites with a better overview of the program.

Basically, they tell the child that when you realize you're lost, you should stop, find a nice tree (or boulder, other large unmoving object), and stay there. Shelter yourself as needed, use your whistle to blow series of three blasts, answer when you hear people calling for you. Stay in place. You have hundreds of friends looking for you, and no one will be mad you got lost. Grownups get lost every day. Stay in place.

For gear, they go very simple. They suggest a large garbage bag or two, and a whistle. Stop hypothermia, get found. Water is a good step, a flashlight too.

Some additional suggestions. Many have noted how frequently adults deceive themselves and rationalize to avoid admitting they are lost. Cody Lundin had a great way to explain to a child how you know you're lost. He said, "You should tell Junior, 'if you look up and you realize that you want to come back to mommy or daddy, and you don't know how to do that, that means you're lost.' "

Fear of being alone is totally natural, even among adults. Lundin went on to say "I think it's psychologically important for a kid to know that he's going to have people looking for him -- not at the end of the three-day camping trip, but that night, before it's dark, and that it's been agreed upon by the family."

Another suggestion from Lundin (and Doug Ritter) is to let children know that when they're in the woods and need help, the usual "stranger danger" rules do not apply. Even adults lost in the woods can get disoriented and frightened, and there are examples of adults not responding to searchers, and even hiding from them out of fear. If children hear their name being called, they should respond.

I think the fact that you've talked this over with your son, and hopefully practiced, put him way ahead of the curve. Reinforcing that he will be found and that he has a job to do to help it happen helps keep him focused. On a recent camping trip, my 5-year-old's first, I had him carrying a very similar fanny pack, his "Hug-a-Tree Pack." The pack stayed on a short branch near the fire pit, and his job was to put it on every time he was walking away from the central fire pit area. Repetition made it a habit for him.

Have a great trip

Dave