Exercise is really good for relaxation and maintaining energy levels and increasing concentration, and also helps you get a good nights sleep (which is really important for effective brain functioning). This year I've been exercising no where near as much as I usually do, but I atleast try to get in 10-15 minutes of walking everyday, even if it's just a walk around the block in a study break.
Umm, I never eat and study at the same time, because if you're eating you're not concentrating on your study, and if you're studying, you're not concentrating on what you're eating. So you end up eating too much and not retaining any information. Instead, I eat during study breaks to maintain my energy/blood sugar levels. When studying, your brain needs regular supplies of glucose to work efficiently. But it's best to eat complex carbs (like grainy breads and cereals) rather than simple carbs (like lollies) because the energy is realeased slower and at a more sustained rate, so you don't get that "high" then crash and burn effect after an hour, but can actually continue studying for several hours.
So yeah, I eat breads and cereals to get my brain working, apples for increasing alertness/concentration, and nuts for quick source of energy when I need food but have alot of study to do to be wasting too much time preparing and eating food.
And yeah, as general overall eating habits: also eat meat or other sources high in protein and iron regularly for energy levels, and lots of fruit and veg for nutrients (keep you from getting sick when you're over-stressing).
Hope that helped
Ha.