what do you do?

I don't get very sweaty on the ride to work, so a quick wipe down with a towel and some fresh deodorant is enough to keep me stink-free. I do keep some baby wipes at the office, just in case. Panniers are a godsend for cutting down on the sweat.

As for the hair, I chopped it all off. The longest pieces are about 2" long, and dry in the time that it takes me to get dressed. A little gel or pomade is all it takes to style. A skull cap keeps the hair from getting sucked up through my helmet vents, and helps wick away sweat too.

Everyone has great suggestions. With only a 3 mile commute, you shouldn't have any problem freshening up.

Here's what I did: When I worked in an office without a shower (only for a year, and then took a job with a bike rack in the lobby and a commuter shower!), I got there early for plenty of cool-down time, kept a small towel and washcloth at my desk, freshened up in the bathroom with a cool washcloth, washed my hair in the sink and blow-dried it (kept the dryer in my desk), and did all the other stuff like makeup, and no one was the wiser. I either brought my clothes with me in a pannier or kept some at work in a closet. I always kept a few pairs of work shoes at work. My commute was 12 miles each way.

I too use baby wipes when I get to work. I carry a messenger bag with a change of clothes, shoes & lunch. I keep makeup at work. I tried panniers, but the wind blows here more often than not and the bag is more streamlined. I liked the panniers because my back is usually sweaty when I get to work and I tried to tell myself that working against the wind will make me stronger, but I usually go for easier! I just make sure that I have about 10 minutes to stop sweating.

I make sure I get to work a good 15 minutes earlier, so I have time to change if needed, and freshen up, and calm down too, if the commute got me working out.
I most often will wear, under my work clothes, a layer that will sort of 'soak up' any sweat, a layer that I can take off once at work. As for my commute back, I don't worry about it since I am getting back home, so getting there sweaty is not a problem.
That layer will often consist of biking undergarments (biking underwear from Juniona and a simple cotton tee).
I hope this helps.