Is there a microwave available in the cafeteria or wherever at your school? If so, it's likely that you can also get free hot water. When I was a student, I always took lunch, and sometimes breakfast, along. And, believe me, I have a tiny fridge, so I won't accept that excuse! The leftovers idea is, of course, ideal. I would also sometimes take instant oatmeal (I know, not the healthiest, but it's better than nothing) add hot water in the caf., use one of those little 1/2 &1/2 things they have available for coffee, and often bring something from home to add. Ground flax seeds, for example: super healthy, $2 for a good quantity at Trader Joe's (keep it refrigerated.) Also, I would generally take a piece of fruit to either eat along with or add to the oatmeal.

I also used to take my own teabags for tea. They will probably charge you a dime for a cup, but I found that better than lugging a mug around in my backpack all day.