The 'Toxic' singer was spotted letting her hair down, just the night before she was expected in Las Vegas to rehearse her single 'Gimme More' with illusionist Criss Angel.
According to sources, Spears, clad in a cream fedora, grey mini-dress with stockings, knee-high boots and long pearl necklaces, settled into a corner booth around 12:32 a.m.
'Britney was in a great mood all night, smiling, laughing, upbeat, she drank beer, vodka cranberry and vodka tonic', US Magazine quoted a source, as saying.
The source also added that Spears smoked a few cigarettes and danced to Rihanna's 'Umbrella.''She was really getting into the songs,' the onlooker said.
Sucking a lollypop, as her new mantra for slimming down Spears left along with Sims at 1:45 a.m.