I use the Topeak Aero Wedge large as well
Usual contents of that are
2 x spare tubes, CO2 inflator plus 2 cartridges, tyre levers, multi tool, bodge kit to get me home.
Emergency carbs - a couple of gels, maybe a snack bar.
Phone
Jersey pockets
BG tester/pump controller
Food - dried bananas, gels, snack bars
Small plastic bag with credit card, café cash, ID
If I were commuting (and I've done this for my runaround bike which gets used for shopping) I'd go with a rack and pannier(s). Also have a small frame pack which sits on the top tube behind the headset, on my recumbent at the moment.
http://www.wiggle.co.uk/topeak-aero-wedge-buckle-large-saddle-bag/
Other saddle bags are available