In practice I don't really need to go very wide. So my 3-piece prime set (on APS-C) usually is:
. Ricoh Rikenon XR 28mm f/2.8. (Had two Pentax 28 2.8 lenses, sold both and kept the Ricoh)
. Auto Sears MC 50mm f/1.7 (also a Ricoh lens), or SMC Pentax-K 55mm f/2 (I have two other 50s I can pick depending on my mood… all 4 get used quite a bit)
. SMC Pentax-A 135mm f/2.8. That one never leaves my bag.
Plus one 52mm inverter ring and I'm all set for macro, too
Sometimes I'll go out with just two lenses, and it works out well. 3 for me is a luxury
If it's just two, it's the 135 I listed above, plus either the Rikenon XR 28, or the Pentax DA 35mm f/2.4.
Finally, there are times when I go out with just one. Camera and lens, that's it (with a full battery of course). That would be the Pentax DA 35mm f/2.4.