Whether on a Pentax dSLR or the small Samsung NX bodies, small and light lenses are great to have on hand. The 16 and 30mm NX are 'prime' examples %( but Pentax also makes small ones - and they even work on full-frame film bodies!
Shown here are the Samsung 30mm f/2 plus Pentax 50/2.8 (1:2 macro!), 100/2.8 and 135/3.5. The K:nx adapter is similar in size to the 30mm.
These four lenses, along with the nx300 and 16/2.4 lens that took this image, can fit into a mighty small space.. And some day soon the NX 20mm f2.8 will join in. The other small-carry option is 16, 30 and 50-200 Samsung lenses, the latter with in-lens stabilization (but somewhat slow at f/4-5.6). Nice choices to have!