I wear cotton or wool (more trousers and long sleeve shirts, than short) unless very warm, or water flying. Leather shoes. I prefer clothing which is less likely to burn, or stick to my skin if burned. My shirts don't have planes on them, as the other planes I fly might be offended.
I will have a high visibility vest or jacket aboard, because if I go down in the bush, I would like SAR to be able to see me. If the airport authority asks me to wear it, I probably will.
I wear a lifejacket for all water flying. In the cold season I will wear a floater suit for lake ski flying, or a full dry immersion suit for extended over water flying.
For one week of flying in 1985, I wore shirts with epaulets and bars, because the Captain handed them to me and said "Please wear these". Other than being asked by an employer, I have never worn bars. I did wear a tie while flying right seat in the corporate Cheyenne for a year, because the employer had a dress code. I respect that, but did not like it!
I wear a watch which is very east to read - it does not have a multitude of minuscule numbers on the face, as I cannot read them anyway, and no one I know would be impressed by them.
And, I wear a David Clark headset, which I bought new in 1983. A really good purchase decision.