Fountain Pens
i can't say enough how much i love these things. get a great one in your nib of choice and include it in your portable sketching gear. for watercolor paper, i prefer a western or japanese fine nib (japanese fine nibs are akin to western extra-fine), and i'm fortunate enough to keep a few pens in frequent rotation: a sailor ink pen, a sheaffer gray snorkel, a sailor sapporo mini with an extra-fine japanese nib, and two lamy al-stars with extra-fine nibs. i warn you, though, that any textured paper is rough for fountain pens, so you want to keep some regular maintenance on them, such as checking for fibers stuck between the tines and flushing the pens regularly. they're also better for the environment, as you can refill your cartridges (with syringes) or converters with your ink of choice and reduce the plastic waste on the earth. i think artists, crafters, and hobbyists use enough paper that this is the very least we can do, yes?