It was, in fact, just last year that, after departing Terminal 5 at Heathrow airport, I realised that my rather expensive laptop was no longer in my possession. In my dazed, fatigue-induced state, I had left it at a Pret a Manger! I rushed back to get it but - surprise, surprise - it was nowhere to be found. As part of the vast majority of people my age who can type considerably faster than they can write, the loss of my laptop was a huge one. At school, I use it all the time for my homework and research, so it's easy to realise how much something like a computer means to me.
This brings me on to my next point: always come prepared, even if it's not the first trip to your boarding school. Obviously, general washing kits (toothbrush, toothpaste, comb, shampoo, etc.) are a necessity, although they can be bought in your nearest town if need be. You can normally purchase stationery from, say, your local WHSmith, so you don't need to fill your luggage with it.
Finally, another must-have item is an interesting, meaty book: if work ever gets to be too much and you just want to relax, there's no better way to do so - especially if you've stupidly just lost your computer.