I think one of the best investments for your bike is to buy a set of Shawlbe Marathon Plus in the biggest tyre your bike can handle like the 700 x 38mm because the investment is better than a headache in having a puncture on your way to work.
Been using Schwalbe tyres on my touring bike for years because they have a puncture resistant band under the tread in which you'll be hard pressed pushing a tack into.....they also have good hard walled sides to stop splitting.
I too highly recommend Ortleib panniers to carry your stuff instead of backpacks and if later you get the urge for some touring, you've got the gear.
Cheers
brumby33