I live and ride with a Fjällräven Greenland size S. Most excellent. It has a kind of second strap that in marketing was touted for cycling, but I find it most useful when walking a lot so the bag stays out of the way.
Quick access is the star feature. I can pull out the most needed things (wallet, phone, keys and insulin) without opening the buckle. That took some customisation though. For car / bike keys I put a ring on the shoulder strap that the keys carabiner on and off quick.