Depends on the location. I like high volume train lines. Back in college, I lived in L.A., and often went railfanning around the Fullerton Station area. Between trains, would casually watch the little league games being played at the adjacent park from lineside, or just people watching at the station. I find waiting for trains to be pretty relaxing- just soaking in the atmosphere of the rail line and surrounding area keeps me from boredom. I now live in Japan, and I don't need any other activities to pass the time- there are so many trains (and all are scheduled to the minute, or even seconds!), that if I get distracted by, say texting on my cellphone, I may miss a train!
-An ex-teen railfan, now just a railfan with a pot belly...