The camera focuses on this car freshener at various points in Ocean's Eleven:
What's the significance of the car freshener?
That car freshener hints at the existance of a certain vehicle that cannot yet be shown to us without spoiling the big surprise:
The car freshener is later shown to be hanging in the SWAT team transporter, which the team uses to stage their getaway with the money.
So even though we cannot really draw any conclusions from this visual signifier that early in the film, it makes for a more satisfying experience to at least have been shown some evidence of something more going on in the background, thus making us feel a little complicit.
It's perhaps a little easier to get a sense of what the writer had in mind from the script notes. The audience is supposed to see the air freshener, then realise that we're looking at the same vehicle later.
EXT. ALLEY - DUSK
Turk and Virgil's white van whips around a corner and shoots inside...
INT. WAREHOUSE - SECOND VAN POV
Of which, importantly, we never see the exterior, just an air freshener hanging from the rearview mirror... The white VAN SCREECHES to a halt inches from Basher who stands ready beside the pinch (and the now-gutted and dismantled mockup of the Bellagio vault) and faster than a NASCAR pit crew Basher, Turk and Virgil load the pinch into the white van's rear and before you can say "electromagnetic pulse" the VAN SCREECHES back out of the warehouse fully loaded.
Later in the script
EXT. BELLAGIO CASINO - NIGHT (PRESENT)- The SWAT team exits and boards the second vehicle Turk and Virgil have been working on all this time, the one in the warehouse with an air freshener hanging from its rearview mirror: it's a replica of a SWAT van.