In Guardian Peak you will meet an NCR soldier who is wounded. Through some Speech checks, you can get him to give you his gun for escorting him out of the cave that he is in. When you get to the entrance of the cave with him in tow, he will speak and you can continually ask for his rifle, which he will give you along with ammunition. Note: This is best done after earning the perk that allows for over encumbered fast travel.
Begin going through the storyline, once you get to Prim and complete the quest there, leave for awhile and return. You will be able to gamble. In order to gamble you must purchase chips. Go to the cashier at the Vikki & Vance Casino. Purchase as many chips as possible with any of the three types of money (Caps, NCR, and Legionaries). Once you have the chips, save the game normally (not by auto-save). Note: Each chip is worth one cap, so you can trade all the chips back for a full refund if needed. Once your game is saved, talk to the cashier again and select the fourth option (something similar to "Cash in my chips"). She will ask what form of payment you want. Pick any option desired, then quickly exit the conversation. This should have given you as much of the form of money you requested that equals to chips. Caps are 1 chip to 1 cap. NCR are 8 chips to $20 and 40 chips to $100, and Legionaries are 4 chips to one Denarius, 20 chips for a Dalhali, and 100 chips for a Aureus. Once you have exited the conversation, check your inventory. You should have the money and the chips still in your possession. Talk to the cashier and repeat the trick. If you want to get higher amounts at a time, do the trick with caps a few times, then buy 1,000 chips for 1,000 caps about five or six times.