I've still yet to meet anyone who ever got ticketed for not having it...I only know about a half dozen guys who have ever been checked without it and they were all just given a verbal warning that they need to get it
I've registered with both NJ and the federal registry since the beginning and have never even been checked
If I didn't have a printer available I'd just take a pic of it on my phone. As long as you can clearly read it I couldn't picture an officer hassling you over it