After having a patch job fail on a tire 12 miles out from home on a cold October evening in the dark, I now carry a completely independent tube and sometimes a tire. Yes, a pain, but I never want to deal with that again. Patching tubes in the cold rain is the pits. Start commuting now, while you can commute with daylight. Night commuting in the rain is a whole nother ballgame with some hefty logistics compared to summer commuting.
One issue some people have is getting up earlier to start a long commute. Have your stuff laid out and ready to go the night before, and the coffee ready to brew if you need that.
Panniers are very nice and allow a lot of heat to spill off you, if you can't take a shower at work this keeps the sweat down a bit. Panniers get stolen immediately if you lock up your bike downtown, so take them with you.
Get a really f-ing bright flashing red led tail light and turn it on all the time.
Get slicks for your mtn bike if that is your commuter. You will find an enormous improvement.
A pair of clear sunglasses keeps road grime and summer bugs out of your eyes.
Get a bike bell. This is nicer than yelling out to people ahead of you that you are there.
Carry a disposable camera. If you commute long enough you will inevitably encounter the bumper of a car. A biker was killed recently in Portland in a hit and run incident.
A chain tool will solve the broken chain issue.
Learn how to repair your bike, completely. If you start commuting in the winter, it will get trashed and you need to maintain it.
Sewer grates are your enemy, as are streetcar tracks.