Believe it or not, this bike is a trek 7.6, so you can pretty much add anything to it. This was my first bike as an adult, and I explained my needs to the bike salesman and the fx series is what he recommended. Unfortunately, once I started riding, my needs changed, but I didn't have money to get a bike more suited to me, so I just rebuilt the one I had.
The things you need... Get a rack if you are going to commute, there are plenty of spots to mount a rack and fenders (if you want fenders), so use them. A rack is pretty cheap, and a backpack-sized pannier shouldn't run too much. And get a saddle pack and stuff a tube, some levers, and a multi-tool in there. I have found that frame pump pretty useful, a topeak road-morph. I can get the pressure up to 100 lb pretty easily, and I think it was only $40. If you are going to ride at night (or even when it starts getting just a little dark) get a light, a planetbike superflash for the rear light is the best buy. I think thats about all the necessary things.
And then there are all sorts of fun things. Probably the best thing I did was upgrade the wheels. The SSR wheels that came with it were pretty heavy, and it made the bike a lot quicker and snappier when I put the Easton Circuits on. The tires that come with it (race lite hardcase I believe?) are darn near indestructible, but a little sluggish. I have gatorskins on mine now, but I get flats. I never had flats with the hardcases, so I'm not sure I really upgraded anything. Next would be a brooks saddle, SO much more comfortable than the one that came with the bike. And I changed out the pedals. The platform/spd pedals that came with it are nice to learn how to use clipless pedals, but I preferred not to use the platforms so I'm using some regular spd pedals. Also, some small barends will give you some leverage on hills and give some different hand positions:
And then there's all the other stuff I've added to the bike, but I wouldn't really recommend doing any of that. I think the 7.6 is a really great bike for what it is designed to do, and I think you will really enjoy it.