Last year I was pulling a gol-darned trailer for all my stuff: gym bag, work clothes, work food, and my emergency kit was basically my entire bike-specific tool box.

This year, I've trimmed it down to where I just look like I'm going off touring: two rear panniers to contain my much trimmed-down gym bag (swimming gear and shave/shower/grooming stuff only), I am leaving some of my work clothes at work; still taking the same food with me (I eat a lot of fresh fruit and veg so an 8 or 12 hour day's worth of food tends to be bulky), and a minimal bike emergency tool kit. I'm also a bit addicted to chains for locking up, so there's some bulk and mass there.

Still, moving down from 4 wheels to 2 has increased my avg mph and shaved a bit of time off, and the panniers are a lot better to drag into a headwind than the trailer.

Maybe some day I will get down to where my commuter bike looks about like a sensible person's weekend bike camping rig.