1. Don't bother with travellers cheques! Take plenty of cash, preferably Egyptian pounds or dollars, although you can change sterling here and there
2. Lunch breaks weren't very well scheduled so try to have some snacks with you. Water is readily available on the buses - when we were there the temperature was mid-forties, so drink at least 2 litres of water a day
3. The sleeper train really is not that great, the food especially, but just take it as part of the experience and you'll be fine!
4. Abu Simbel was well worth a visit, and definitely by air if you're happy to afford it
5. You can leave things on the bus most of the time, so you might want to take a small bag to put a purse, camera and sun cream in. I had a small back pack which I barely used and could have done with a little bag
6. Bring hand sanitiser, immodium, rehydration sachets and keep plenty of Egyptian coins for the toilets!