always a matter of personal opinion this subject. there's a guy on another thread who intends to take a chair with him.
i took a camelbak last time. i didn't use it for water, but it made a good day pack for days off the bike. you would get used to riding with a pack on, but it does get sweaty in the summer....
personally i think an air mattress is very unnecessary. i tend to take a rug for cowboy camping (nothing like sleeping under the stars) and some bubble wrap for under my sleeping bag on colder nights. i doubt you will have too many cold nights on your trip though.
water depends on services and heat. for one desert section of the southern tier in august, i took about 3 gallons. i like to have at least 3 quart bottles on me all the time. going thirsty can be dangerous and at the very least uncomfortable.
i do take a bike lock for urban areas. never bothered with bag locks though. noones ever stolen anything from me, but i hear it does happen. actually a raccoon once managed to open my ortliebs and steal some cookies.
to charge electronics, i checked into a motel or "proper" campsite every few days. it's a nice treat to look forward to a shower and some comfort too