So your dad kicked you out of the house and you have to survive on your own. Once you are done screaming at your dad you can actually do something productive.
-9mm pistol: Assuming your dad isn't the biggest dick ever, he probably gave you a 9mm pistol. These weapons are simple and cheap. With fairly good durability this weapon will allow you to take down many enemies that aren't very well armored, like Miss Petunia who yelled at you when you tipped her Brahmin.
-Varmint Rifle, Service Rifle or Cowboy Repeater: This is from worst to best, a varmint rifle can usually be found in a shop and are very cheap. A service rifle is harder to come by but with good durability you can fire it all day, the New California Republic uses this weapon, why shouldn't you? Finally the Cowboy Repeater is the best you can get without having to pay an arm and a leg. It's fairly good damage and pretty high durability make this gun only topped by the Hunting Rifle. At least on the lower levels, when a majority of the other rifles come into play.