I haven't bothered to put racks on my Tricross Comp yet, so I carry a small backpack with clothes (I leave my shoes at work), towel, body/hair wash, tube, multi-tool, phone, wallet, keys, iPod, and food if I'm taking my lunch that day. Probably a granola bar or Clif bar too.

On days I have to bring my laptop home, I just slide it in with the clothes/towel. I keep an extra power cord at home.

I wouldnt' carry much more even if I had a rack. I'd like to have a camera with me, but it's not allowed in the buildings where I work and I can't leave it on the bike.