Hi there! I totally identify with exam season. One more to go for me (Monday), then I'm finally done with grad school!
I'll second Ron's advice to remember to enjoy yourself come Christmas eve dinner; holiday season is a crummy time to start a diet, and plus, the whole point is to be thankful for the food on your plate and celebrate being with family. Don't be too hard on yourself if you gain a few pounds over the holidays, it happens to the best too.
Exercising outside (or even getting motivation to drive to the gym) can be tough in crappy weather, so there's lots of bodyweight movements you can do in the comfort of your own home. I wrote a fitness program on this thread
that you can do indoors without much equipment (just some dumbbells or your loaded up backpack or a small animal) and it's got some inherent variety so you won't get bored. And, it will definitely help you get "toned" (there's no such thing as real "toning," the effect comes from a combination of muscle building and fat burning that makes that area of your body more shapely).
Good luck with finals, and happy holidays!
1) eat real food - more vegetables, moderate meat, moderate fruits, less grains, less sugar, less vegetable oils.
2) exercise - moderate intensity cardio, sprinting, heavy lifting, dedicated stretching and mobility.
3) live - relax, de-stress, meditate.
Disclaimer: I'm not professionally qualified to make any formal recommendations. I've just done my homework and I'm my own guinea pig. All of my data, unless otherwise cited, comes from a sample size of n=1 (me).