Held Up (1999)

While they're on vacation in the Southwest, Rae finds out her man Michael spent their house money on a classic car, so she dumps him, hitching a ride to Vegas for a flight home. A kid promptly steals Michael's car, leaving him at the Zip & Sip, a convenience store. Three bumbling robbers promptly stage a hold up. Two take off with the cash stranding the third, with a mysterious crate, just as the cops arrive. The robber takes the store hostage... (imdb)