OK, So don't laugh. Here is my Plein Air art supplies
and how I carry them.
Ivy has a back pack and she carries all the little stuff.
Small sketch book, paint box, a couple of brushes, a pen, pencil, tissue, her water and dish. I carry my camera, larger paper and/or a larger sketch book and my water. If I am going to be out all day, I have a chair that has a shoulder strap.