Mischa Barton -- That's How She Rolls

2/16/2010 3:05 PM PST
Mischa Barton was driving around aimlessly in her classic Cadillac yesterday in L.A., smoking some sort of roll-up.

Mischa -- who pled no contest to DUI in 2008 -- got sidelined after running out of gas.

As for what she was smoking ... no word yet from her rep.