Quick question, do I have to EARN the voucher, or USE the voucher in order for them to be valuable in the BoS bunker? The wiki is a tad unclear on this point..
You have to win 7,500 chips at the Sierra Madre casino to get your first voucher. When you've done that and return to the Mojave, you get new vouchers good for 1,000 chips each in the bunker drop box every three game days.