I'm not saying it's not necessary items, but your list isn't what I consider packing lightly. Although "lightly" is a subjective term and what you consider the bare minimum is probably different than what I do.

As I mentioned already, my load varies from day to day due to my ever changing work locations. Today I had to bring clothes (underwear, socks, pants, shirt, belt) and my shaving kit. I already had my towel, shoes and food at work. Despite this, I don't consider this a light day even though I was able to easily fit it all into my backpack. Kind of a "medium" day.

Especially compared to Wednesday where my backpack contained exactly one wallet and one yogurt. My work location was close enough to home on that day that I showered there and wore my work clothes while I rode. I probably didn't even need to bring a backpack but I didn't have anywhere else to stick the yogurt.

However, I certainly have my "heavy" days too. There are days where I have to haul my clothes, towel, shaving kit, food and perhaps shoes too. Those days I usually take the bike with panniers as it's a bit much to fit it all in a backpack.

There are even days when I have to haul specialty items that require me to pull a trailer. Thankfully I only have one or two of those days each year.