Finally, at good old Opus, I found the Sooke Mini Table Easel for $25! I filled it with 3 Niji waterbrushes (these are genius for al fresco watercolour painting! They hold the water in the brush handle, simply squeeze), 25 Sharpies (so many colours! and they don't run when you paint over them), 2 bamboo mechanical pencils, kneaded eraser, watercolour pencils, all of which were chosen for their portability. And a sketchbook with heavy paper that can withstand a lot of water without getting wrinkled.
I love it because he can use it at home, but we can take on adventures and document what we see. Our first adventure was on Christmas Day. It was a wee chilly. Next time we will bring gloves.