Mark, you need a supply of containers from large ice cream tubs to old plant pots to one of those long plastic window boxes, drill holes in them, thread some of that strong nylon rope through the holes and either carry them up or pull them up once you're up there.
You need to fashion a few hooks like a butchers hook that you can put around the top rung , or hang off a branch and put your paint, paint brushes, tools and general stuff into the handiest tub, so when you're up in your tree ( or wherever) you've got all your screws etc up there with you. I've had a piece of rope tied to the top rung for years now with a metal hook on the end... Perfect!