One of the many challenges of painting outside is protecting yourself from the elements. I wear an old pair of blue jeans, some comfortable shoes, NOT sandals, and an old paint shirt. The clothes should not be too bright. You can get reflected light from your clothing onto your painting surface. This will interfere with your color choices. I like to layer my shirts. Sometimes I wear a t-shirt under my painting shirt and sometimes a tank top, depending on the weather. I also carry a spare long sleeve shirt and jacket in my car.
I have a favorite straw hat to protect my head from the sun. It has a fold down brim I use when it gets really hot! I carry a spare hat in my car as well. I also pack bug repellant and sun screen!
I have not found an art umbrella I like yet. This will be the next addition to my set up. I am looking for one with vents, not a problem but how to attach it or support it is the challenge. If all else fails I can always use the tailgate of my "Art Mobil".