Re exercise: Good point, but I'd emphasize making a strong habit over doing it a lot. Spending a lot of time is easier during summer, but harder to carry over. Sure, do that, but also make sure you have a 15 minute routine, say, that you do every morning. Even a five minute routine isn't to be sneezed at, if you're doing bodyweight exercises like pushups.

Doing a stretch and 5 minutes of exercise during study breaks is worth a try. Could help avoid some of the physical problems with long hours of computer use. (Press down with your whole hand during pushups - strong fingers, hands and arms will help avoid RSI.)