A good trip begins with a good plan. I usually start at least two weeks in advance with an Internet search looking for relevant railfan pages, timetables, maps, and the home pages of companies operating in the target area. The truth is out there! I will try to accumulate as much as I can carry, reviewing it in detail while in transit. If serious fannin looks to be on the agenda I will pack two cameras, 100 channel scanner, portable mobile antenna, construction grade footware and research documents. If it looks like fannin opportunities might be limited a single camera and the scanner might be all I would want to carry. I always seem to travel with the scanner.
A spare camera and plenty of film can save considerable time in areas where you don't know whats available. Extra camera batteries should not be overlooked.