A couple of months ago when I stayed at Red Rock in LV, they were giving away gift cards good for $10 in Shell gasoline. You could get up to 3 a day based on player points you racked up. The nice thing was it didn't consume any credits; you just asked for the card.

I've used my gas credits but if anyone collects things like the logoed envelope the card came in, let me know and I'll send you one.

It's possible this promotion is still on. If you play there in the near future, it's worth checking out at the promotions booth.