You might be tempted to serve Carne Asada with refried beans, and of course you're free to do what you want. But in Mexico, "We eat beans all day every day! For Carne Asada, we just want meat." (As told to me by many Mexicans in Aguascalientes.) So, for the most authentic experience, stick to classics like grilled green onions and chiles, guacamole, and super simple quesadillas.