I have a bag, I don't give a flip what anyone says, thinks, feels about my bike. It is 900 degrees in the shade in the summer, I don't want all that crap in my pockets like DH does. And I secretly snicker at the people who do, sorry ladies/guys who look down on my bag but I am laughing on the inside at you in all my fredom!
I have a mountain wedge but eventually I will get off my lazy bum and put the new bag my SS sent me last fall on it, it is nicer but I need to mount something to put it on. 
Both are big by roadie standards but pretty modest. I carry a tube, CO2 cartriges and pump, house key, Aleve canister, emergency tampon, tube patches, lip balm, tire levers, tiny thing of sunscreen. I have a black berry which won't fit so it rides on me with my "shoe wallet" style wallet. My bag is stuffed to the gills but I don't want anything bigger. I carry my food stuff, maps and sometimes camera in my pockets. That is already too much stuff.
Amanda
2011 Specialized Epic Comp 29er | Specialized Phenom | "Marie Laveau"
2007 Cannondale Synapse Carbon Road | Selle Italia Lady Gel Flow | "Miranda"
You don't have to be great to get started, but you do have to get started to be great. -Lee J. Colan