Below is my present set-up for doing plein air. I have a half-french easel in which I store my oil paint tubes, two side trays, a paper pallette, an Art Comber (from Jerry's that has large wheels to go over any terrain easily,sets up 18” off the ground, and has a waterproof bag that I can put my easel and trays into), and a backpack in which I carry my liquids, pallette, apron, paper towels, brushes and drawing materials. When I paint, I use the pull out drawer to hold my medium (in a baby food or mushroom jar) and mineral spirits (in a Creative Mark brush washer which has a very tight sealing lid, essential for an medium.), plastic gloves and plastic shopping bags for trash. The pale blue box below the canvas is an old wet wipe box and instead of wet wipes, I cut my paper towels to fit and put them in that, weighted by a nice piece of coral. Leaning up against the tree you can see my wooden wet canvas carrier that could carry two wet stretched canvases and has protected me from getting more paint on me when I am transporting my artwork from the field. It has a nice leather handle on one end and is really lightweight.
Before I got the half french easel, I used a regular french easel, a french mistress (wood box with two wings that fold out from jerry's) to hold my paints, a paper palette, and a luggage carrier to wheel it all around (using bungee cards to hold everything onto the cart). I had a huge insulated picnic type bag in which I carried my liquids, apron, and everything else. I decided to go smaller with the easel because it was lighter and luckily, I could fit everything else into the backpack that came with it AND do without the extra weight of the french mistress.