Fallout: New Vegas/The Legend of the Star

Some bottle caps have a blue star. These Sunset Sarsaparilla star bottle caps are considered rare, and are associated with a legend where you can collect a treasure if you collect enough of them.

Some time after you grab the first bottlecap, you will encounter Malcom Holmes, who will tell you about the legend. He will describe what they are, and warn you that there are some people trying to steal them.

The star bottle caps may be located at the following places:
 * 6 are found on Malcom Holmes. He approaches you some time after you collect the first cap.
 * One in The Devil's Gullet, inside a box.
 * In the Lucky Casino in Primm, on a desk across from the elevator.
 * Up to 9 bottlecaps from Tomas and Jacklyn fighting near Nipton. If Jacklyn survives, you can kill her for the caps (or combine it with an Intelligence check for some experience). Otherwise, you have to pass a speech check, pickpocket or kill Tomas for the caps.
 * One inside Nipton, in the house across the Nipton Trading post. Found on the bedroom shelf.
 * In Camp McCarren, by purchasing from Contreras.
 * One in the wreckage east of Nipton (on the crate)
 * In the Fields Shack, inside the fridge.
 * One in Cerulean Robotics, in the break foom to the right on the entrance. Look on the table.
 * In Aerotech Suite 300, on the kitchen counter.
 * In REPCOMM Headquarters, in the first floor office.
 * In Sniper's Nest, near Cottonwood Cove.
 * In the Bitter Springs recreation office.
 * Two in the Callville Bay Boat rental office. One is on display, and the other is next to the cash register.

There is also a 5% chance you can obtain a star bottlecap each time to drink Sunset Sasporella.