Drive-Thru Britney -- Shhh!

Britney Spears, with baby on board, was snapped on her second run (in two days) to a Carl's Jr. drive-thru.

Wearing what appears to be the Wal-Mart wig knockoff of Posh Spice's bob from last season, topped with a short-brimmed Panama hat (is the hair attached?) and metallic safety goggles ... the pop mom drove thru -- with Sean Preston sound asleep in the backseat. Keep it down, y'all!

The former Mrs. Federline is now a working single mother of two, with an active dance rehearsal schedule, who clearly doesn't have time to cook! Gotta go, y'all!