I have provided links with suggestions for brand, but that will be up to you. (Click links to go to retail websites)
If you already have equipment comparable to anything on this list, feel free to bring that instead. If you can't get the supplies on this list then bring what you have.
PLEIN AIR BOX or EASEL Your usual Outdoor Painting Rig
I wrote a blog post about plein air easels here: Plein Air Rig Blog Post
Sketchbook, Pencils and Sharpener.Two black Sharpie markers.
Cheap Canvas Panels (like you might find at Michael's or Hobby Lobby.)
At least three- 4x6, 5x7 and/or 6X8
At least three- 8x10 or 9x12
Bring canvases as they are. (White, with no color on them.)
Two Palette Knives. (Avoid very small knives.)
Paper Towels (I use Viva because they cling to themselves when working in high wind.)
Bug spray, Sunscreen, Hat with brim.
Coat, Jacket, Rain Jacket.
Wear neutral colors, nothing brightly-colored, prefer grey or black.
Bring at least 5 brushes of the same size and shape (Ex: five #4 flats). The brand is up to you. I use Utrecht Flats, mostly hog bristle, can be synthetics but hog is cheaper. A hog/synthetic blend works well too. (Don't have to be new just clean).
And possibly one - #4 Rigger for detail and signing.
Buy the largest tubes you can afford. (150 - 200 ml) You will save money in the end.
Cadmiums are stronger colors. More expensive, but will also save you money in the end. I use mostly Utrecht colors.
Black Paint (Ivory Black preferred)
At the very least, 3 Primary colors (Yellow, Red, Blue)
Ultramarine Blue (I use French Ult. Blue by Winsor Newton)
Utrecht Titanium White (You can also use a less expensive Utrecht Studio Series Titanium.
Cerulean Blue Hue
Phthalo Green(Student grades work fine for stains.)
Yellow Ochre (Student grades work fine for stains.)
BRUSH CLEANER / SOLVENT
I recommend 20oz Anderson 3-latch containers. (nothing smaller and nothing less than 3-latches!)
Mona Lisa Solvent from Michael's is cheap.
If you have allergies you might try Gamsol or Turpenoid.