Figured I would turn to the experts here instead of randomly buying something that I probably would hate or wouldn't work. I just bought a masi special CX for my commuter and love it. I'm looking for a bag to go on the back of it, maybe a large saddle bag? I commute 7 miles to work and need to fit; 1 pair of pants, shirt, belt, dress shoes, and 2-3 tupperware stuff for food. Is there any large saddle bags that will fit this? I'm looking at this option because i don't want to buy panniers and a back rack, cause on the weekend i wana be able to just take off on the bike with no load. Also something that matches the old school aesthetic of this bike.

heres my bike for reference: