I use the Kelty Ridgeway 2L hydration pack for my commute. Just take the bladder out 95% of the time but it’s handy to be able to put a blader in there now and then. Not sure if they still sell it…but it’s perfect for a change of clothes, a lunch, some hygiene equipment, plus extra room in the mesh side pockets if you want to stuff gloves/arm warmers/leg warmers in there.
Not sure they still make it, though. But if you can find one it will last forever.
I see there are some on ebay for about $40. Don’t know if I’d pay that much for it. But the form factor is perfect and the durability is good…so, maybe.