I use both a keyboard and a guitar for most of my jobs. To save weight and pieces for the "one-nighter-singles", I use a nylon string directly into a PA.The on-board pre-amp and effects in the PA seem to do the trick for me. If I use a steel string or an electric (Parker Fly is the instrument of choice), I use a San amp pre-amp. It' not ideal. If I have the room and the strength, I use a mid-80's Fender super Champ lined out to the PA. For my jazz trio, I use a Polytone and an L-5 or the Parker Fly. For variety/dance music, I use a Super Reverb with a 335 or, again, the "Fly".
As I get older, the equipment gets lighter. Soon, I be playing a kazoo!
Russ