Pregnant Jessica Simpson Eats Grilled Cheese, Onion Rings, Avoids Alcohol at Pal's Birthday Bash

Jessica Simpson visits Macy's South Coast Plaza in support of the Jessica Simpson and Jessica Simpson Girls Collections on November 10, 2012 in Costa Mesa, California. Credit: Jamie McCarthy/Getty Images

Jessica Simpson knows how to make the most of a cheat day.

The Weight Watchers spokeswoman -- expecting baby no. 2 -- went all-out at a December 2 birthday lunch for BFF CaCee Cobb, 35.

"Jessica ordered a grilled cheese sandwich with onion rings," a fellow diner at the Polo Lounge in Beverly Hills tells Us Weekly.

As her friends toasted Cobb with cocktails, the mom to Maxwell, 7 months -- who has yet to confirm her pregnancy -- waved off her usual white sangria.

"Guess what?" she told her server, with a smile. "I'm drinking ginger ale!"

In anticipation of the baby's arrival, Simpson, 32, and fiance Eric Johnson, 33, are in nesting mode: A source says they just made an offer on a house in L.A.'s luxe Hidden Hills!