I am off to London tomorrow for the weekend and my mate wants to take in a Millwall game.
I was going to book the tickets online but they wouldn't get to us in time.
I'd assume it's the same as most football clubs they have a ticket office you can just turn up to and purchase a couple of tickets on the day of the game?
Get yourself to the ground early doors and sort it out. To book in advance you need to register but I think you'd be able to do this in person too. I'd give the ticket office a call and double check first.