Go to Primm, and successfully complete the quest to get them a new sheriff. Wait a few days for NPC's to spawn inside. Then, go to the Vikki and Vance Casino. Either win as many chips as possible from gambling or buy as many chips as possible. Go to the cash register to trade the chips in for caps. You will get the equivalent for the chips in caps, but you will still retain all your chips. Simply keep trading in the chips for caps to get as many caps as desired. Note: This glitch was done on an unpatched version of the game.
Go to a weapons and/or armor merchant, and see if he has two of the same weapon or armor for sale. If you can afford it, get the overall most expensive item at the lowest condition. For instance, if he has two Raider Sadist Armors at 45% and 76$, but also has two Flamers at 20% and 8%, then choose the Flamers. Purchase the cheapest of the two items, and then immediately sell it back to the merchant. Buy it again, and sell it back to them again. Usually the second, but sometimes the third time, you buy the same item from them, and it will appear in your inventory at 100% condition. Sell it back to them, and it will reappear in their inventory at the original low % condition. Buy it again, and it will appear at 100% condition. Repeat this until they have no more money. Note: This glitch can cause the game to freeze. It is recommended you save your game often when doing this just in case the game freezes.