Panic.
After I panic, I sit down and write out everything that needs to get done. I take the major items and break those down into little to do lists and give everything a due date.
All of that panicking and list-making sure has worn me out. I need a break. So I take a short break, put some music on (usually this or this), and start tackling that seemingly never-ending to do list.
How much I do every day or week is really determined by the due date. If it's a semester-long project, I try to spend about 30 min a day on it and an hour a day on Saturday. If it's something due in a week or so, I try to spend an hour a day on it, broken up into two 30 min sessions.
And, when all else fails, I panic again.