Compact brushes are often super expensive in the art store, and often very small in size. Being the cheap guy I am, I got some lipstick form dollar store and turned them into my compact watercolor brush.(those are number 12 brush in the photo.) It is not only compact, one would never have to worry about messing up the hair when the brush is retracted and capped. Total cost of the brush is about $15.(Brush is about $12, the lipstick was $2.25, plus the cost of glue and cleaning supplies.)
I think anyone who love to sketch on location should totally do this too!!!