I'd agree - the best thing to do is make a photo copy (laminate it if you can) and keep it in your boat. That's what I do with my fishing license so I'm never without it.
My wife just got her certificate and she's not around right now for me to ask her what would happen if you get caught without it. Maybe they'd punish you by making you swim home or worse yet, they'd force you to say your ABC's backward.