Ideas in letting people watch a game only if they have paid to watch it?

We are planning a game night at a local shop. People are only allowed in if they pay to watch a game. We need ideas on how to do this. For example like when people walk in and pay should we give them a number to know they paid already. Or put them a wristband as an id showing he has paid. Its kind of like a walk in pass. We are doing this so we know everyone in the shop has paid to watch the game this is for a fun raiser.Ideas in letting people watch a game only if they have paid to watch it?give them wrist bands that way no one can give them to friends or what not and sneak it. anyone not wearing it gets kicked out