I tried to paint in my A3 sketchbook while standing up. It was a disaster - here is how:
First I decided that I would hold both my sketchbook and a jar with water with one hand. This meant that after the first few minutes, my hand was so tired that I lost control of the jar with water and it flipped and drenched the whole spread with slightly green water. Like this:
After this I decided to not show my frustration to my companions and see if I can save this sketch by throwing everything at it at the same time and limiting the time that I would give it. I declared that I'll be done in 5 minutes and I used my fingers and whole palm to paint quickly. Like this:
Here are some process photos and results: