Spears dons a cowgirl hat for a shopping spree in Beverly Hills. Plus: Gwyneth & Apple, Lindsay Lohan and more

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SISTER ACT

Meanwhile, Ashlee Simpson checks out the scene at new Hollywood restaurant lounge Parc with a pal on Saturday. As for big sis's new guy John Mayer, a Simpson pal tells PEOPLE, "Ashlee loves John. She thinks he's great for [Jessica]."