So, don't spend 2 hours on a sketch. Spend 15-30 minutes.
2. Next, I just use a little pocket paint set. While most of the cube Cotman colors have been replaced with M.Graham, still, not fancy. Not for real paintings.
It's the only pocket paint set that separates out the paints that I could find. Most would have you swimming with muddy pigments - bare bones is fine, but it must be workable.
3. Finally, I paint in my lovely journal. The handmade paper is gorgeous but doesn't erase, respond to overworking or many layers well. Basically no sizing. Perfect to be forced to work quickly.
I rarely paint on the back of sketches, so I could tear out a major disaster. That hasn't happened yet, but plenty of blah... But I'm not going to tear apart my lovely book to hang them on the wall either.
Sketching is immediate. You usually won't produce great art in a sketch - but you will produce much better art from a sketch. It forces the artist to really see and experience their subject. Sketching is the best way to improve your art - lots of good practice!