In-N-Out's menu is straightforward. You probably already know exactly what to order. Incase you have never eaten there, you can look at this menu. And yes, it includes their "secret" menu. But if you're arriving during a rush, you will have plenty of time to decide.
Here's what is important to take away: you might reach the front of the line while your driver is still trying to find a parking spot, and another friend is trying to find seats. So you need to know their orders so you don't hold up the line. Don't be that incompetent person who still doesn't know what to order after spending all that time in line. Customers are hangry, employees are tired, and if you read the People section of this website, you know the risks.
You'd think we wouldn't have to explain this to anyone past the age of 9, but surprise! People are horrible. We want to make sure you have manners. Have you witnessed customer meltdown in a restaurant? Not pretty. So, here are some things to keep in mind: