I would say that I play live a lot of the time without any pa system at all. This is usually doing solo spots during our Welsh MVC concerts each month. So I would be playing/singing to audiences of 70+ folks in hotel function rooms, village halls or churches. It is great to turn up and play with just your guitar - nothing else!
Where I need some "lift" such as small bars, pubs ect I use my Rode NT1a ldc mic', plugged into whatever pa the venue has. I have just ordered a new cheap mic' - Lewitt LCT 240 pro with cradle and wind shield - and a very compact mixer - Sub Zero SZMix04. I have a couple of powered speakers, so I'm going to see what I can do with that simple set-up (mic - mixer - powered speakers) as a complete system for gigs where I need to provide the pa. I sometimes play/sing with a friend as a duo, and running just one stage mic' to cover instruments and vocals for us both is a great set-up for that type of performance. It looks good on stage and really makes the most of being an acoustic "duo" - plus it make singing close harmonies together much easier than using two mic's.
I'll be interested to see how the Lewitt LCT 240 Pro performs. I contacted the company in Vienna, Austria a couple of months ago to ask about bluegrass single mic'ing a stage, and they suggested their cheapest mic' as being a good option! It does seem to have a good cardioid pattern at all frequencies, so I'm expecting to just have to roll a little off the top to get a high level of gain before feedback from it.
I have been trying to find a Behringer FBQ800 compact e/q to help ring out any room but they are not available new at present. I have the Ultragraph Pro, so that will do the job but it is quite big and stereo (which I don't need). For single mic' stages you can sometimes run a slightly higher volume in some rooms by using a 15 band e/q to ring the room rather than the two or 3 bands on a compact mixer. I have a Behringer FEX800 so I can chain that in if I find the single mic' is a little dry in a room.
I think that the Lewitt LCT 240 Pro into a small acoustic amp (set forward of the mic' line) could be a really nice set-up for those "coffee house" gigs. For some acoustic amps you may need a compact mixer (like the Sub Zero) to provide 48v phantom power. Anyway, I'll know after I have tested it.
The other rig that I use is two dynamic mic's - one up one down. 58 for voice and 57 for guitar. If I need a little more headroom for say a Friday night pub then this is what I will go for. I always seem to get plenty of push from mic'ing my guitars. I know that it is not popular here on AGF - but I wonder if that is simply lack of familiarity with using a mic'? As I have said before, I think that the way you use a vocal mic' determines how well you can balance a mic'd guitar. It's not rocket science, but it is science. Sound falls away by the square. You can't be on top of the vocal mic' and get a guitar to mic' well. But if you are 8" off the vocal mic' then using a mic' for guitar becomes really easy.
I don't have a rig for plugging in my guitars.