Arizona Scavenger

 is a free quest in Fallout: New Vegas.

Quick walkthrough
After speaking with Aurelius of Phoenix at Cottonwood Cove HQ, he can offer you a cap bounty for NCR troops that you kill. For proof you have to bring in NCR Dog tags.

Optional you can change the money reward to ammo and supplies. For that, go to Decanus Severus. For the locations of dogtags, head over to locations with a heavy NCR presence.