I just got one of these. After a couple months of commuting with it, I am very happy.

https://www.rei.com/rei-garage/produ...2-cycling-pack

The no-zipper top is excellent. It comes with a (yellow) waterproof cover in a dedicated pocket. I have used that two or three times and it works great. The pockets are good sizes. It has a dedicated space for my u-lock.