Simpson, 33, and fiancé Eric Johnson, 34, are hosting an outdoor Independence Day party for all their wedding guests at the San Ysidro Ranch in Santa Barbara, California. The family-friendly affair comes the day after a small rehearsal dinner took place at the same location.
"We’re having a real Americana 4th of July party," says celebrity event planner Mindy Weiss, who organized the stars-and-stripes-themed gathering. "It’s very down home. But it’s not a T-shirt and jeans Americana. Because Eric’s from Boston, it’s more khakis and white shirts. Very Kennedy!"
The pre-wedding party includes a cocktail hour with passed appetizers including lobster dogs and corn fritters, plus a shellfish station.
Then everyone will line up for a Southern-inspired buffet where beef brisket, smoked barbecue baby back ribs, fried chicken and grilled shrimp will be served, along with side dishes such as mac and cheese, coleslaw and potato salad.
For dessert, guests can indulge at a pie bar that will offer slices of apple, pecan, key lime, peach and coconut cream pie. Or, for something cooler, Bomb Pops, Creamsicles and watermelon are other options.
(And for anyone worried about the bride-to-be's wedding waistline, which she whittled down with the help of Weight Watchers, just remember she looks like this.)
Partygoers will also be able to enjoy a photo booth, games for the kids – including the couple’s daughter Maxwell, 2, and son Ace 12 months – and, of course, sparklers to mark the national holiday.
Overall, the festivities "have a carnival feel," says Weiss.
"Jessica didn’t want her guests to miss out on the 4th of July," she adds. "That’s who they are. Their No. 1 concern is for their guests coming all this way for the wedding."
For all the details about Jessica Simpson's wedding – and her exclusive wedding album – pick up the new issue of PEOPLE, on newsstands Friday!