My hat is essential! I also try to layer and wear long sleeved linen shirts that I can roll up in the summer. I have gotten so many bad burns that I am paranoid about covering up.
I did three seasons in Greece, which was actually the best in terms of climate. Super hot but almost no humidity. The worst thing there was scrambling through thorny maquis all day.
Nowadays, I do my work in Ontario.
I wear jeans and steel toes if I am going to not get wet or am doing 1x1s or shovel testing, but if I am excavating burials I go for a pair of zip-off light technical pants because I usually end up barefooted trying to balance over the feature and flexibility is key then!
When I have been out in the fall/early winter, it's all about warmth. Long johns, trousers, over trousers of waterproof breathable fabric, boots, various woollen layers on top and a windbreaker shell and then a down parka on top. Oh, and fingerless wool hunting gloves. That way if I am digging I can strip down for high output, but when I am sitting in the freezing cold or rain documenting a burial while my hands freeze solid I need passive warmth. I still remember late October 2010 as being particularly miserable.
I don't know about you, but if I wore full on movie arch gear, you'd be teased mercilessly. I help out with annual field schools in addition to my professional work and it is always interesting to see the first few days how people show up to work. Usually skimpy tank tops but their first giant burn usually dissuades them after. I know they look at me all swaddled up brandishing a bottle of suncsreen and think I am being ridiculous
I'll see if I can find some photos.