I've been commuting for 30 years, and for most of that time, I was commuting without a helmet, handlebar bag, seat bag, extra tube, multi-tool or a tyre gauge. Most of my commutes were done with a bike, a frame pump, a tube repair kit and lights. That's really all you need. The other stuff is good, but in essence, the bike is a tool that you use to get from point A to point B. It doesn't need to be complicated.

I scorn bike clothing! If you can't bike in jeans and a T-shirt, you're turning a commute into a hobby or a sport. If you want to do that, fine. But it's not necessary.