I have 5 laptop bags (every time I go to a work conference or vendor fair, I win another bag!!!). Three are messenger style bags and two are backpacks made with padded laptop compartments. I prefer the backpacks. I used the one I bought until I won another one that's better and smaller (my new laptop is 14" widescreen, so it's tiny). I walk around a lot and I prefer a backpack b/c it doesn't make one should ache and make me slouch like a messenger bag does. I also prefer the backpack for carry on when flying.
This is the backpack I used before I got my current one. It was like $35 new at CompUSA and that was 3 years ago. I had a 15.4 laptop at the time and it fit perfectly. My new backpack would be too small for a 15.4.
http://reviews.digitaltrends.com/images/reviews/1047/20040126_1917591.gif
I used to use a wireless mouse and I ditched it b/c it was a pain in the ass. Maybe they make them better now, but it was too annoying have to always have a receiver sticking out of the laptop, taking up a USB port. Plus, anytime my comp was asleep or the lid was shut, it would take a minute or so for the receiver to kick in before the mouse worked. If I used a regular USB mouse, it works immediately b/c it doesn't need to re-connect itself to a receiver. I liked my mouse and it was really cute, but after the batteries died the third time I stopped using it. I've become so adept with a touchpad, I can do photo edits and manipulation in PS and FireWorks without a mouse.
Other laptop accessories I use.....
* lock
* something to keep it cool. I used to use a USB cooling pad, but again I needed that USB port for other devices so now I simply prop up the laptop in the back with a mousepad I cut into 4 pieces and stacked up. Keeps the air flowing underneath and makes it more comfortable to type.
* I wish I had bought a second power pack b/c I hate having to unplug it constantly going between home and work.
* I use a card reader on a daily basis b/c it's faster than my camera and doesn't waste the camera battery. My laptop has a built-in card reader, but not for CF cards which is what I'm using at the moment.
* I'm going to get one of those skins you put on the back/top of the laptop to keep it from getting scratched. My laptop has a really shiny surface so even the tiniest scratches are noticeable.
* I keep a pack of anti-static LCD cleaning wipes and wipe down the whole laptop once a week. It keeps from getting the nasty wrist marks built up.