Be prepared!
The sites in Luxor are nothing short of spectacular so it is best to be organized.
A flashlight! It is dark in the tombs and the lights don't always work either because they don't or because the caretaker can't be bothered with turning them on.
Plenty of small bills. Parting with 1LE bills is almost the cost of being a tourist in Egypt and can magically open 'closed' tombs, light up dark chambers, or get rid of a particularly pesky tout.
Water. Water is available outside most of the sites but not always readily available inside.
If you don't know your Osiris from your Anubis, it might be a good idea to read up a bit before you go. Otherwise, you'll wonder what the fuss is all about!
the Colossi of Memnon, free admission, view from the roadside