+1 on the bento box (stem/toptube bag). I have a RavX one, and I find it to be invaluable...especially on those days that I wear tops without pockets. I have quite a few bike "tops" (can't really call 'em jerseys, since they don't have pockets) that I like to wear on warmer days - they fit looser and I feel more comfortable in them on a hot and sticky day.

Anyway...I generally put all of my nutrition in my bento box, as it's just easier for me to get to, since it's right in front of me...instead of having to reach around and fumble in my rear pockets while riding one-handed (NOT my speciality! ).

I can easily fit a full size Clif Bar (or 2 mini size), plus a package of chews like Luna Moons, Clif Shot Bloks, Sharkies,etc., as well as a few Newtons in a snack-size ziploc. Even with all that in there, I still have room for some chapstick, a small microfiber swatch to clean my sunglasses, and my cellphone & house key.