In reply to Matt Rees:
I carry laptop, phone, wallet, puncture kit and other bits and bobs in a small rucksack. Berghaus Remote 25, as it happens (although in market for a new one), as it has nice cooling channels on the back. Everything inside in plastic bags if any chance of rain. Laptop in a padded sleeve to protect it. £5 Aldi hi-viz rucksack cover over it.
I prefer a rucksack to panniers, as it's narrower through traffic and the bike is more manouverable - 11-miles each way, so not too bad on the arms. I don't carry enough to fill 1 pannier and wouldn't want the weight lopsided. Laptop size means putting it on top of a rack isn't ideal - too vulnerable if I come off.
You can fit a pannier rack to a bike without lugs, using a normal rack with P-clips round the stays or I've used this one on my Trek:
http://www.blackburndesign.com/en_eu/racks/rear-racks/ex-1-disc-rack.html - you'll also need one of these (or similar) to fit your bike:
http://www.tredz.co.uk/.System-EX-Seatpost-Clamp-with-Rack-Mount_62152.htm
I keep spare shoes and trousers at work and take shirts in on the days I have to drive in. Lucky enough to have showers at work, so keep towel and toilettries there. Bring everything home now and then for a wash and polish.
I also keep a bike lock at work, so less weight to carry.
Use whatever you like as rear lights, just use a road-specific front light with proper beam pattern, rather than a dedicated off-road floodlamp.