Do not send a pair of good trainers or shoes for wearing for dry activities, doesn't happen, so shoes that can wet and wellies.
Get a permenant marker and write his name on everything, I mean everything. Like if they have to take a water bottle write it on the bottle and the lid, on pants, tea towel, torch, sleeping bag. Everything, the will lose stuff but at least the leaders will know it is his. Good idea to let him help with this or at least watch so he knows where name is written.
Munchies are a must, enough to share is a good way to make friends. Like multi pack of choclate biscuits.
Pack P.Js on the top so they are easy to find when going to bed, they are likely to sleep in their clothes unless leader cateches them.
If he is used to a pillow its an idea to put in a small cushion or something.
Make sure you are clear what kind of roll mat to take, some try to take inflatable matresses and they take up too much room, my DS didn't use his inflatable mat as he thought he wasn't allowed, no idea what he slept on that camp. Inflatble roll mats were allowed.
If you have a chance get him a wind up torch, they always fall asleep with them on and batteries are done on the first night otherwise. Can be got very cheap.
Teddies were require by all boys on DS's camps, I thought that was a great idea. DS still takes a couple to scout camp, one is a mascot but they other is def a cuddly