I know the "3 lens kit" question is a common one, but I become obsessed by it sometimes. I'm pretty happy with my 135 and 6x7 3LKs, but my APS-C kit is tough.
For 135, I use a 28/50/85 setup and am very pleased. I don't do macro or tele here (much), so this really meets my needs. However, my go-to lens is the M40/2.8 if I have to just take one. Great focal length, tiny lens. Love it. Unfortunately, this film setup doesn't translate well to APS-C.
My 135 setup would equate to 18/35/55 in APS-C, with a pancake 28. Fuji has almost this exact combination available for their X cameras! If I were rich, I would definitely be looking into that system. But I have most of what I want currently, and enjoy being able to play within the entire Pentax ecosystem--from Q to 6x7--so I'm not going anywhere.
Anyway, fun question, and one that I've devoted too many hours and spreadsheets to!