Boomerang covered a lot of things already (thanks Jason!), but I want to expound on a few.
I recommend around $20 in singles for vending machine privileges. Most crew trainers (counselors) will reward their team with a trip to the machines for a job well done or good team work. There is some mystic appeal towards Dippin' Dots!
As far a gift shop/souvenir money, I
highly recommend putting his spending money on his account. When he arrives at camp he will receive a plastic, waterproof wristband with his name, team and room assignments and a barcode. The barcode will access any money on his account, allowing him to spend that money in the gift shop and at the concession stand at the IMAX theater (which he will attend at least once during the week). The amount you put on his account is completely up to you. You can go on the Space Camp website and take a look at the prices of selection of the items available in the gift shop.
There are a few optional things you can order and pay for in advance, such as his flight suit or clothing package, his team patch and a DVD of photos taken of his team all week. As Jason mentioned, the flight suit is a wonderful souvenir, but won't be worn during the middle of summer when it is very hot. The team patch is an awesome souvenir. As a mom, I highly recommend it! The team chooses a design from 9 set designs, then the last name of every one on the team is embroidered around the outside. It's a pretty good deal for less than $15! The photo DVD is another thing to consider. Each Crew Trainer is issued a camera for their team. The CT takes photos of the activities throughout the week. These are then downloaded and burned onto DVDs which can be preordered, purchased at graduation or ordered later (we still have almost all the original DVDs since we started that program). Kids bring their own cameras to camp, but when you put a camera in the hands of a 10 year old boy you're just a likely to get 50 photos of the inside of his left nostril as you are of his camp experience!!
What to pack: be sure to pack things that you won't mind never seeing again. He will have wonderful adventures in survival and crawling around in the woods on his belly. Sometimes the clothes are beyond salvage by the end of the week! Send old sneakers too, for the very same reason. It makes my heart ache when parents send their children with all new clothes for camp! Also, do not send him with his Gameboy, etc. First off, he won't have time to use it during camp. We keep them busy from sun up to well past sun down. There is no 'down time' for our kids. Secondly, it's an easy item to lose. I'm amazed at the parents/kids who never call looking for the $$$ game that got left behind. Last year we donated 4 Nintendo DS's to a local charity. They'd been sitting in lost and found for over a year! Be sure to label everything he brings with him. Put both his first and last name.
As Jason said, our Crew Trainers are wonderfully trained to take care of your son and help him have an amazing experience. He will be teamed and housed only with boys of his own age range. If he's 9 you don't have to worry about him having to uphold himself in a pack of high schoolers. He'll be with other 9-11 year olds. The activities are geared to that age group.
Always feel free to call Camper Services at Space Camp (256-721-7185) with any questions or concerns.