Personally:
1. Kindle Dx - not having to take my whole library from Austria to England back is a real live saver. Additionally many of the books I need are freely available in the Kindle Store. The bigger screen makes it also more useable to read PDFs compared to its smaller brother.
2. LiveScribe Smartpen - I am a fairly slow note-taker. So, this is gonna be a life-saver. Records all the lectures and makes them easily replayable by clicking a certain part of my notes. Great for revising as well.
3. (Portable, ie 14" or smaller) Laptop - Not much to say here. This is a must have for me. No use taking a 20" monster to uni.
4. Smartphone - I love my iPhone and could not do without it. I can do almost anything with it. Of course another brand might be just as good. Take whatever you like best.
5. Good calculator - At least if you have Maths courses. Take one you can actually control.
I can't think of anything else right now. A printer might be useful, but that is personally too bulky to take on a plain. Other than that, sturdy shoes, winter coats, bottle openers and all that stuff - not really gadgets in my opinion.
Edit: A good navy blue suit might also be worth bringing. Takes you from the welcome dinner with the provost to the job interview. Also not a gadget though.