Going to Vegas how should me and my girlfriend spend or money?

Me and my girlfriend are going to las vegas in June for 3 days sunday through wednesday. Its $700 round trip with hotel (MGM Grand) and 2 free tickets to any show we want. I was thinking one of us can pay the $700 for the trip and the other cab pay for expenses in vegas is this a idea? Ps my girlfriend makes more money than I do I'm basically broke.