What if uninvited’s just show up!?

I’m actually concerned that a few of my guests will just bring a random person without rsvping for them and just show up... but how are you supposed to navigate that? It’s not like you have a bouncer at the door making sure people are on the list and kicking the rest out. Also, I plan on doing a seating chart... and those surprise guests won’t have a seat or a plate of food nor do i want to have to pay for them when they weren’t invited! My ceremony and reception are in the same place so I’m not sure what to do if this happens!