A puncture repair kit (they come pretty small - I have one as big as 2 fingers put together). Tools - you really only need 3 - tire levers, an allen key, and one of those multi-size wrenches. Chain oil is also an essential every 200 miles or so, but not something you need to take with you on a ride.
I have a little tool bag that clips under the seat. It's about big enough to fit the repair kit, tools, cell phone keys and perhaps a trail bar, but that's about it.
You can get water bottles and holders that clip onto the bike frame.
In terms of learning basic maintenance tasks, try bicycletutor.com/
Edited by: MOTIVATED@LAST at: 7/8/2013 (23:08)