I am making a cake for someone and they want to know if I can put something bwtween the layers for moistness that they had years ago in their wedding cake, She thinks it was coconut and something else. i have no idea ? anyone? 

Could be anything.  As a example, the coconut and pecan filling in a German Chocolate cake is very moist.  I am making a coconut and lime cake tonight and it has a cream cheese lime and coconut filling.  Google coconut fillings and see what you can come up with.