Planning first overnight bike trip with son. Any suggestions?

As the title says, planning an overnight bike trip on the Great Allegheny Passage for me and my 10 yr old son. We will be tent camping at a KOA. Some other kids and parents may join us, but for now we'll worry about ourselves.

Equipment - he has a Haro Flightline 24" MTB, 21 speed. Mine is a 1990's vintage Mt. Shasta MTB. Both bikes in good mechanical condition. I will also be towing a trailer similar to the bob-yak.

We will be covering 20-25 miles per day. Not much, I know, but I don't want to go crazy on the first trip, and I want to give plenty of time if we want to stop and check stuff out. Also, the second day is going south into Ohiopyle which looks like it has some grade to it. He averages 11mph on most rails to trails paths, so I don't think I'll have a problem keeping up even with the extra load.

Need to get the boy a new helmet. Any suggestions for brands that are comfortable, light weight and not hot in the summer?

Here's what I figure we need to take: Repair kit - air pump (looking at the topeak pocket rocket. any opinions on that?), assortment of wrenches, tire levers, spare tube for each bike, patch kit (is there much of a difference in patch kits?) Anything else I'm missing here?

Foul weather gear - rain coats, poncho, etc. First aid kit. Phone, gps, printed maps. Normal camping gear, stripped down to the basics for weight.

What are your thoughts on bags to mount on the bike? I don't have a rear rack, and I don't know if panniers would interfere with the trailer mount. I'm also concerned about balance if I have a handlebar mounted bag vs. a frame mounted bag. I have the trailer to haul most of the gear, but I want a few small bags for repair kits for my usual rides and general carrying. Any brands to avoid? I like to be thrifty, so I don't want to buy the cheapest crap that's going to fall apart, and I don't want to spend more than I need to.

Signalling devices - horns, bells, yell "get outta the way!"? What do you use.

Headlights- not planning on riding at night, but better to have and not need it. Again, looking for something better than a harbor freight flashlight and duct tape.

Sorry this went on to be a huge first post here, but I figure it's better than asking a bunch of individual questions and clogging up the works.