I am grateful for these helpful responses. Thanks for taking the time to write.

I actually have two bikes to ride this summer: a Trek FX 7.3 for my daily commute and errand running, and a cannondale R600, which I acquired about two months ago for road riding. Last year I took the Trek on 3 rides of 75 miles each and one century. Since these were solo rides, I had to take everything with me. I packed food in my panniers and took four bottles of liquid (water and gatorade) in a small insulated cooler strapped to the rack. This summer the cannondale will be my horse - no rack, no panniers. Anything I take will be in a back pack. I have opted for the Camelbak Rogue, 70oz, which will, I hope provide a compromise of volume, weight, and a little space to carry my spare tube etc. I also have a fanny pack that I might end up using. I am not a racer - I am training for distance.

Thanks again for your help!