Your FAK should be consistent with your training, which is the most important component. Mine tends to be heavily weighed toward trauma and I don't carry that many pills for indigestion, etc. Many items (splints, for instance) can be readily improvised. With training, and just a bit of experience, you will have a pretty good idea of what are the most useful things to include in your kit.
Needless to say on this forum, it should be as lightweight as possible. Did I mention that training is important?