I'm sorry you have to go through that, but it's better to get the ball started now. That way, your parents can have their input on things, and it'll be an easier time for you (as much as can be, anyways) when that time actually comes. One good way to look at it is, at least you won't be wasting time arguing with your siblings and other relatives about how the headstone/grave marker should be designed! Some of my cousins had that problem when their brother passed unexpectedly, and they argued for about a year before deciding on something.