I usually fill at home and carry 2-3 pens if I'm going to a conference or something where I may write a lot. However, if I do need to fill on the go, I carry ink vials instead of bottles (the smaller vials don't need a big, clear space to be used for refilling) and a couple of wipes. Dip the pen, suck up ink, wipe the section, done. I usually don't even get any on my fingers, and if I were really worried about it I'd carry ink nix or amodex to wash it off before it stained.
