I've tried the backpack. I have an average 1 hour 40 minute multi-mode commute each way and there is NO WAY I'm gonna put up with a backpack and those hassles that long.

I use 2 Topeak racks. A quick-release beam with side frames, and their standard Explorer, depending on the bike I'm on. With the Topeak's biggest trunk bag that has the built-in panniers (that zip/fold out of their built-in side pouches). They can easily hold laptop, complete set of clothes, lunch, and way more. And if you only need just one pannier, all the better (folded back into pouch -- no sail). I love that "slide-and-slam" motion that locks the bag to the rack. Guess I could gently latch it, but the "slam" is just fun. I do pull out the built shoulder strap at times - love how that attaches to the bag.

I'm at least 4 years into using that MTX bag / style and can't imagine using anything else unless I get into self contained touring. I'm a credit card tourist at this point.

My other rack/pannier rig is the Xootr CrossRack (built expressly for the Swift folder) and matching eleven-71 bag. Now that's a real sail, but it's amazingly versitle. It will easily hold a 12-pack and complete fixinis for a steak dinner for two. A laptop and clothes are not a problem.

I DO use a backpack with my bike that LIVES at the office. I'm happy using it for short jaunts to the grocery or hardware, on the days that I arrived by car. I'm very lucky to have indoor storage for a spare bike. That's a feature !! Some days I just arrive early and ride for an hour or so. Normally leave the backpack at the office for those rides.

Good luck getting settled in.