Bring or arrange to have a shooting mat. Even if you don't employ the thing in the standard manner, it can make a weird-shaped rock into a very workable supported position.
You covered hydration and sunblock and hats, so that's good.
If you wear contacts like I do, have adequate changes to cover each day you'll be there, as well as eye hydration and contact rinse. Eyes and ears are important, protect them at all costs. Wind and sand defy even very good eye protection, so have a way to get that cleared up ahead of time. There are precious few times that we go cold range, so have good hearing protection on your person at all times.
Bee & wasp spray would be nice to have on hand, not an issue in Spring but definitely a needed feature for Fall.
Temperature can fall off pretty steeply at night, pack something warm because the really interesting conversations happen in the coldest part of the night and you don't want to miss out.