High season on the Nile runs from November to February, and the reason is the afternoons: dry, still, and somewhere around twenty-four degrees when Luxor in August would be closer to forty.
The catch is the drop. Desert nights shed heat fast, and by ten in the evening the deck can be near nine degrees with a breeze on top. A linen shirt is not going to do it. Bring one genuinely warm layer — a wool jumper or a light down — and you will use it every single night.
The rest of it
Shoes that you do not mind scuffing: temple floors are uneven, sandy, and occasionally slick where a million hands and feet have polished the stone. A hat with a brim all the way round, because the sun is directly overhead at the exact hours you will be standing in an open courtyard. Sunglasses that you can afford to lose over the side.
For Aswan and the Nubian villages, shoulders and knees covered is the courteous default for everyone. It costs you nothing and it is noticed.
Leave the drone at home — it will be taken off you at the airport.