Well you could buy the shop and still get it wrong. Start simple and build up. Start with the odd one or two day adventure. Most people can exist for that long without missing most things. But the basics are the same for most outdoor activitys. Keep dry and warm, keep fead and watered, be comftable. And most important everything you need must be caried and it weights twice as much at the end of the day, so throw half of it out now to save time. The new fabics are so good now that a good three layer system can stand up to a lot of weather and still be light and free moving. Tents are so light and easy, so you could get a two man for when the son joins you. Get a catalog from some one like Field and Trek as they have good guidance on equipment in the back. But don't over do it you will never need half that you could buy. Don't worry about being to specialist about the gear. And good luck I think its a great thing for a son and dad to do.
I tried one of those water proof bags that are ment for money and small items. The small camera fitted fine but when I fell out of the boat there was just too much water. So the tip is make sure the bag is big enough and well sealed. If you are going near big water make sure the bag is up to the job. But for rain and stuff then the zip seal bags should be okay. There are some bags about A4 size with a zipper, which you can get from office suppliers. Leno
I know this is a bit late but next time try rice. It is great at absorbing moisture. Just put the item in a air tight container, margarine box, icecream container, with a load or rice. Then gentley warm, sunny window sill should do. Leave for a day or two then as if by magic it should be dry. Might be a good idea not to eat the rice.