I don’t get how you can make bicycling your only form of transportation, even if the bike travel infrastructure and parking is adequate. When I bicycle, even for a short amount of time like 15 minutes, I sweat, and end up a stinky wet mess at my destination. Especially in the summer. My shoes and pants get dirty from the road and my hair gets wet and messed up especially if it’s raining. So if I’m going anywhere with…
These cities are relatively flat, relatively cool (watch videos of cycling in Copenhagen and you'll see a lot of people in coats and hats), and you don't have to bike very far to get somewhere interesting. There's also the fact that there's a lot of bikes on the paths (which, for me, caused me to slow down considerably from my typical bike pace when I visited). This all combines to mean you aren't putting anymore effort in than a short walk: you just end up going a little farther in the same amount of time.
Re: the rest.
When I was a regular cycle commuter (in a Canadian city) I did pack a change of clothes, spare deodorant and/or wore a removable outer layer that resisted road gunk. Road gunk is _much worse_ on any route you share with cars. Dedicated bike paths tend to be quite clean. Paniers are far better than a backpack, since they sit on the bike frame, you barely notice the weight. But as other commenters noted: a little fitness goes a long way. After a year of commuting, my regular route wouldn't even cause me to break a sweat.