Seating and painting support
The simplest solution would be a folding chair or stool and something to paint on like a portable easel or lapboard. You could being a second chair and lean your drawing board against that. You could also use a folding table.
There are a variety of pochade boxes, portable easels and painting systems available. You may be able to find something used or make your own.
Sun protection
Though it’s recommended to be in the shade while painting, both for comfort and to keep from painting too darkly in the intense light of the sun, it’s also wise to consider other forms of sun exposure protection: hat, sunblock, or painting umbrella. I use one of these UPF rated adjustable golf umbrellas: Sport-Brella (Amazon link).
Other outdoor concerns
Drinks, snacks, insect repellent, or anything else you might normally consider for spending a few hours outside.
