My personal play list is over four hours long and has about 150 songs on it. That includes vocals and strumming, folk vocals with fingerpicking, country blues and ragtime fingerpicking solos, and Hawaiian slack key instrumentals in 5-6 different tunings. I can do - from memory - about an hour's worth of each category. But I have been playing for a LONG time, performed for many years at coffeehouses and festivals, and routinely play in at least three different jam circles therefore I need to know a wide variety of songs. While I practice a lot, I don't learn very much new stuff these days, as most of my practice time and attention goes into maintaining what I already have under my fingers and in my brain. And yes, if you don't play it somewhat regularly (at least once or twice a month) it goes away. In my case, the music itself is fairly easy because I can hear chord changes pretty well after all this time, but I find myself needing lyric sheets and set lists a lot more than ten years ago. If I have a gig coming up, I will spend about 90 minutes per night for a couple of weeks beforehand polishing up what I plan to play.
I always suggest to students and newer players to have five of your favorite songs that you can play from memory on demand, and keep a 3x5 card in your case with that list. In a song circle or jam, it takes a while to come around to you five times, so you should be covered. Odds are you won't have your binder, your music stand, a light and all the "stuff" with you around that spontaneous campfire jam. At every guitar camp or major jam session, there is always a song or two that I don't know but want to be able to play, and I make it a point to go home and learn it the next week. Then it becomes another song to maintain.
