TM has discussed sharpeners before, like the folding pocket sharpener and Carbee, but Smith’s PP1 Pocket Pal Sharpener includes carbide, ceramic, and diamond options. And, as the name might suggest, it fits in your pocket. Both the carbide blades (for quick edge setting) and the ceramic stones (for finishing the edge) have v-shaped slots, and are reversible and replaceable. The 400-grit diamond tapered round rod folds out and can be used on both standard and serrated blades (or to smooth out that nick in the rim of your favorite beer glass). The PP1 is available on some sites for $7, but the shipping will likely overwhelm that price unless you buy some other stuff.
Is this multi-function sharpener useful enough to carry in your pocket (or toolbox)? What do you think?