Multiple orders

Normally when you go through drive-thru you only have one order (yours), and if you have multiple people/orders you come inside. Our dining room closes at ten o'clock, so all we can do is take drive-thru customers. It's understandable if people need to pay separately because they have two separate methods of payment, which is when I don't mind making two orders. What irritates me is when customers surprise me with it. Sneaking it in right before they're done, like they think they're slick or that I would have said no if they had told me in the beginning.

Me: "Is that everything?"

Customer: "That's everything for the first order."

Me: "You have a second order?" *facepalm*

Customer: "Yeah."

Me: *wanting to bash head into register* "Okay, go ahead."

There's only two things worse than that:

1) Springing the second order and paying both orders with cash when you could have combined them and just had one order. This is a little bit ridiculous, don'tchya think?

2) Springing the second order, not being ready with your money and then paying for the second order with the change I gave you back from the first one.... 

^Perfect face for that situation, lemme tell ya.

ARE YOU SEROUS RIGHT NOW. I ought-ta slap you. What was the point of that? Wouldn't it have been easier to just make it one order?

I don't particularly like taking two orders, but if you tell me in the beginning, it's a little easier on us, and we can have both of your orders ready when your car gets to the window.