I always envy people who can do everything with a single ballpoint pen. But for those of us who carry sketchbooks/notebooks around, a subset of us are Multiple Utensil People. If I'm sketching, I like to use a 0.3mm for interior linework and dimensioning and a 0.7mm for outlines and titling. When writing out plans in a notebook, I like black ink for the bulk of the text and red ink for the crucial bits.
British architect Michael Ruthenbury is an M.U.P., and for himself and the rest of us, he has designed the Flipclip, a handy way to keep your multiple preferred mark-makers on hand:
I cam't say it's the perfect solution—my notebooks tend to live in a bag, and I imagine the protruding Flipclip might "hang up" on the other junk in the bag when I try to pull it out—but I think it's a step in the right direction.
Apparently, fellow Multiple Utensil People agree. The Kickstarter campaign has been successfully funded, with $14,904 pledged on a $7,484 goal. At press time, there were just four days left to pledge for the $11 object.