On the left side of the rack I use a large Ortlieb office bag for miscellaneous stuff, papers, iPad, journals, cable lock, and there's room leftover.

On the right side I use an Ortlieb shopper for layers that i shed on the warmer ride home, and stuff I pick up on the way home - light shopping, mail. I could probably jam everything into the office bag, but I like the convenience of extra space.