Being a natural klutz, I prefer two panniers, even if they're pratically empty individually as I distribute the weight between the two. I rode with one initially, with a basket on my rack, but I kept the weight down until I got two.

While I have campus pedals on my commuter (flat on one side, SPD on the other), when I'm actually carrying a load I or commuting to work, I don't wear cycling shoes - I wear regular flat shoes. Again, I'm a klutz and with a load I don't want to have to worry about clipping in and out and being unbalanced.

When it comes to what I wear, I usually wear "normal" clothes when running errands - usually it's light weight hiking type pants (more breathable and quick drying) and I can zip off the leg. I do wear more cycling type clothes when commuting to work because I often combine commuting with my workout and take a longer route home and/or ride harder. Often I'm just running out the door to quickly go get something from the market, though, so I take off in whatever I happen to be wearing