My commute items: appropriate lighting, good reflective night vest, reflective tape on my bike. Pedros "Trixie" fix gear tool (first class!) or 6" crescent wrench (I used a Sears 6" for about 25 years). 2 tire irons, 2 tubes (bad days happen, keep 'em in a sock to protect them from your tools), patch kit. My keys on a good pocket knife or Leatherman. Hex wrenches for the fasteners for that bike. (Loose wrenches are far easier to use than ones on multi-tools.)

The next to smallest underseat tool bags hold all this easily. Eight miles is roughly the average of my commutes over the past 45 years.

Ben