Experienced travelers to Egypt consistently say the same thing after their first day: they packed too much and brought the wrong shoes. I'll give you the short list first, then explain the thinking behind each item.
Shoes: closed-toe, with a sole that grips uneven stone. The floor of the Valley of the Kings is not level. Some tomb descents require stepping over carved thresholds. Sandals work in cities; they are a liability underground. If you own walking shoes that have covered a full day's walking without blisters, those are the ones to bring.
Sun protection: a hat with a brim, sunscreen SPF 50+, and a lightweight long-sleeved layer. The linen sold in Luxor is excellent for this — breathable, loose, and it dries in twenty minutes. Many of my clients buy a galabiya on their first day and wear nothing else for the rest of the trip. I am not against this.
Water: I provide water for my clients throughout the day. You should carry at least one litre independently — especially if we are walking between sites. Dehydration starts before you feel thirsty. In summer, one litre per hour is not unreasonable.
Camera: bring what you actually use. A phone camera is fine if that is what you know. A heavy DSLR lens that you carry but never change is weight you will regret by the fourth site. I time tomb visits for the best available light and position you for the angles worth taking — the equipment matters less than the moment.