A farb is someone who doesn't care if they're authentic or not. You might often see such a person wearing modern cowboy boots and cowboy hat with their poorly-made uniform.

As far as guitars in camp... well, it depends on the camp. If you're talking about soldiers on the move, probably not. If you're talking about a garrison camp, maybe so. Garrison camps often had civilian visitors so in that situation you might find things you wouldn't find in a campaign camp.

If you're talking about a civilian refugee camp... depending on economic status, some people fled their homes with every darn thing that would go in the wagon. Others had no more than the clothes they were wearing. So there are a lot of variables to consider.