This thread got me hooked on IMDB trivia and I found something pretty interesting:
According to writer-director Edgar Wright in the DVD commentary, when Ed attempts to cheer Shaun up at the Winchester with plans of binge drinking, he is actually summarizing the events of the next day (Z-day) entirely in drinking references. "Bloody Mary" - Checkout Girl, "Bite at the king's head" - Phillip, "Couple" - David and Di, "Little Princess" - Liz, "Stagger back" - impersonate zombies, "Bar For Shots" - firing rifle.
Just goes to show the intelligent writing in the film. That's what I love best about it!