Doc Mitchell can be lied to, then he must be convinced with a Medicine skill check of 25 to provide aid for a "hurt traveler down by the highway".
If lacking in the appropriate skills, one can always buy the supplies, pickpocket the doctor, or simply kill the doctor and take the supplies.
Head over to Joe Cobb and give him the supplies, and help the Powder Gangers attack Goodsprings. Most non-player characters in town will become hostile, but one will receive assistance from several Powder Gangers. If not killed previously, Doc Mitchell, Easy Pete, Trudy, Sunny Smiles, and Cheyenne will gather around the Saloon and fight the Courier and the Powder Gangers.
Once the residents of Goodsprings are dead, one can talk to Joe and claim the reward.
Whichever quest one chooses to complete will affect reputation with both factions and simultaneously cause one to fail the opposing quest.
If Joe dies during the course of the attack on Goodsprings, but the attack is successful, then the quest will end once all hostile Goodsprings inhabitants have been killed and grant the XP reward to the player character. No further reward is obtainable since Joe actually dies (instead of just being 'unconscious') and cannot be spoken to. [verified]
If the player character has already spoken to Ringo and agreed to help him, Joe Cobb will dismiss them when they try and ask to help him take over the town. Each time he is asked, he will claim he does not like the look of the player character.
If the player character has killed Ringo previously, dialogue options allow them to immediately begin gathering supplies.
Once this quest is completed, the surviving Goodsprings citizens will sometimes say, "That was a hell of a way to repay Doc, if you ask me." when interacted with.
Chet does not take part in the fight, and still runs the general store after the quest is completed.
Both Ringo and Joe Cobb will talk about Ringo's relative safety hiding out, saying that Ringo could shoot Joe Cobb through the windows. However, the windows on the outside of the gas station are boarded up, and there are no windows in the interior of the gas station through which Ringo could shoot or see anyone coming.
Two small dialogue options were cut from the quest, pointing to an additional task Joe would have asked you to perform: freeing the town's bighorners. While Joe's responses are not present, presumably this would have been intended to create chaos in town. The option was likely removed owing to the presence of free-roaming bighorners in Goodsprings in the final release of the game, although Joe still mentions this when you talk to him.
PCPlaystation 3Xbox 360 When the player character kills Ringo and inform Joe Cobb, he will ask them to get supplies from Chet and Doc Mitchell. Before getting supplies one can kill Joe and fail the quest, but Chet and Doc Mitchell will still be locked in the 'Help the Powder Gangers' dialogue speech, and one can get infinite experience, leather armor about 1/2 repaired, 30 9mm rounds, and Powder Ganger fame. (See Fallout: New Vegas exploits.) [verified]
Playstation 3 Sometimes, the mission will not complete. Even though the Courier has killed every citizen in Goodsprings, Joe Cobb will still say that there are people to kill. When attempting to talk to Chet, he will simply say, "Can't talk now, there's a gunfight!". The mission is stuck in this limbo forever. This issue may happen because Doc Mitchell is stuck inside his house. The player character will have to go in and kill him themself to complete the quest. [verified]
PCPlaystation 3 Occasionally the player character will not be able to loot Doc Mitchell's body if they kill him. Saving and reloading does not fix this bug. [verified]
PCXbox 360Playstation 3 For some reason during the quest Run Goodsprings Run, if the player character kills Ringo and takes his deck of Caravan cards, it may freeze for a couple seconds and make the noise like when scrolling down the Pip-Boy menu, then stop and one can take the rest of his things. It does not seem to cause any problems other than freezing for a moment with the noise. Caused by each individual card being added to the player character's inventory. [verified]