Jamie Lynn Spears celebrated her Big Day with fiancé Casey Aldridge shopping at Wal-Mart and having dinner at Ruby Tuesday.

We support whatever makes America’s favorite unwed teen mom-to-be and teen baby-daddy happy.

“They both seemed very happy and in real good moods,” a source tells of the couple’s outing near Aldridge’s home in Liberty, Miss.

“Jamie Lynn had a big smile on her face.”

With Wal-Mart purchases in hand, Spears, who is pregnant with Aldridge’s child, took in a quiet dinner with Casey, 18, at a restaurant.

“It was just the two of them,” says the source.

“They were like a little adult couple, very low-key.”

Meanwhile in Los Angeles, Jamie Lynn’s big sister Britney Spears gathered with the rest of the Spears clan for a family dinner in Los Angeles.

Britney, parents Lynne and Jamie and brother joined a group of about 10 people for an Italian feast at Ristorante Peppone in Brentwood.

“Britney was in a great mood, and had dinner with her family and friends,” a restaurant source said.