That's not much, a lot less than I carry--but I'm a beast of burden. (I notice, no bike tools, unless they're in the red bag?)

I think any small backpack will work nicely for you. Try to find one with a laptop compartment (for the paperwork) and a large main compartment (rather than lots of smaller compartments). Some are more durable than others--look for metal zippers, or at least the heavier nylon ones. Bright colors are good for cycling, and I think they look jauntier also.

This is a great time to buy a backpack because of back-to-school sales. You will find an excellent one for under $30.