High Sierra has a lot of great versatile backpacks. I use when for work commuting. My son uses one for high school that has been very durable and has a padded laptop pocket.
www.ebags.com has a great selection for great prices. Get one that has a belt strap and a sternum strap. This will increase stability of your pack. Then...important "then"...go to Amazon and buy the Camelbak backpack rain cover.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1 I use one to protect my clothes when I ride to work. NEVER had a problem when caught in the rain.