I have a tiny seat bag with just a tube and a patch kit. I actually wish it could be smaller.
That way I can take as little with me as the weather and ride require, or a bunch if the weather looks changeable.

Your comment does remind me of Spingineer from another forum here. We joke about his chipmunk cheek jersey pockets. It's amazing how much he's willing to stuff into them.

I do admit for a double century I switch to a really big (at least for me) seat bag that is so very ugly. I even strap on a "bento box" just because when I'm out for 16 hours I want clothing options and food. Maybe even a camera. By the time I get all that, plus lights, on my beautiful Roubaix it starts to look for like a street person's bike, with all teh clean lines gone and covered with clutter.