camelback... power-type bars...
yes on the camelback idea here too!
Had the camelback for almost a year, then went out one day without it and realized how hot it was on my back. I now have a 70 oz Platypus bladder & tube in a big fanny pack that I wear low on my hips. The fanny pack actually keeps the water quite cool, has more room in it for keys, phone, etc (all in ziploc baggies of course!), and keeps my back cooler than the camelback backpack. If you've already got a big fanny pack, the bladder and tube were less than $20, so it was a lot cheaper than buying one of the camelback fanny-pack styles... just be sure that the fanny pack has load-balancing straps like a backpack would...
I agree on the power-type bars - I usually cut mine in half ahead of time, then put 'em back in the wrapper.