I usually shop online for parts. For example...I paid $9 for a f-ing 29er tube at a local bike shop that shall remain un-named. Same tube online was $3. Nashbar, Bikeman, Jensen, REI, Amazon, etc all have good deals.
In my Camelbak you will find a multitool, tube, toilet paper, hand pump, CO2 w/inflator, tire levers, tube patches, bug spray, small thing of sunblock, food stuffs, my wallet, cell phone, emergency whistle, SRAM power links, and a 15mm wrench (if I'm taking out my singlespeed).
During the summer the big bladder is a must. Not a bad idea to have an extra bottle of something on the frame as an emergency reserve if you run out.