Here is a sure fire way to tell if you ride goofy or regular.
Get a razor scooter. Hold on to it and run super fast with it, jump on and start scooting with what ever leg you are most comfortable with. This will make your subconscious kick in and tell you what leg you want to lead with and what leg you want to kick with.
Your kicking leg will be your back foot (or power foot) The foot that you put forward to steer the scooter will be your front foot.
This will be the same on your snowboard.
Now that you have figured out what way you ride, have a beer because the hard part is over (at least it is until you decide to learn switch)