When I had to wear suits at work I wore a backpack. Didn't like it cause it made my back sweat, but didn't really have a choice. Luckily we switched to business casual for the summer so I just rock a handlebar bag with items I need, patch kit, shoes and lunch. I'm really happy with it and I sweat less from not having the backpack holding in all that body heat.
I tried a Carradice Nelson once or twice a while ago but didn't like the way it made the bike feel. Felt like it slowed down its handling. Guess it would be fine if you had a casual commute, but cutting in and out of traffic I needed the bike to respond quick.