I'm thinking about buying a Martin backpacker guitar for traveling (it would be small enough to fit in an overhead compartment and looking at airlines' websites seems to indicate that most or all will allow it to be stowed there). Of course it doesn't have as full a sound as a regular guitar and isn't as loud. It would cost about $150. Chris Monti has one and it seems to be playable, although a bit finicky at times.
On the one hand, I'm not sure how often I'd use it, but on the other hand there are times when it would be really handy. Hmm.
I'll think about it and decide whether or not to get one when I go to my accordion lesson on Tuesday, I guess.