For what its worth:
I cannot commute to work each day, I'm a field engineer and I must travel in multiple states within a days time. However, I travel to the grocery store and purchase my groceries via a bicycle. Its amazing how that will limit you buying junk food! LOL
helmet: Don't leave home without it.
front lights: 1 on helmet and 1 on handle bars.
rear blinkies: Mars 3.0 on bike and a small blinkie on helmet too!
fenders: you will appreciate them greatly.
Rear rack: with basket and 2 panniers (one on each side). I've also just ordered a backpack.
I have two bikes - one mountain and one hybrid. both have disc brakes! Going is optional, stopping is not! I think I prefer the hybrid. Because I like the workout it gives me and its comfertable.
That is really about all my list I can give. However if you notice I've stressed safety in my ride. I don't have any highways to travel on, it's mainly back streets and trails. Hope that helps.
I have yet to purchase any tools because I only travel about 2.5 miles to/from the grocery store. However I take a cell phone with me incase of mechanical breakdown. If its 90 degree out and I have milk I don't want to change a tire, I'll just call the wife and tell her to bring the truck.