Level up Endurance
Take the Toughness perk
Take the Life Giver perk
Take the Adamantium Skeleton perk
Take the Chem Resistant perk
Take the Rad Child perk
Take the Old World Gourmet perk
Take the Implant GRX perk
Get the Endurance implant from the New Vegas Medical Clinic
Wear armor with higher Damage Threshold to survive longer
Use food, chems, and stimpaks to stay alive longer
Use companions to reduce incoming damage
Take the Intense Training perk and raise Endurance
Use the Small Frame trait only if you do not need extra limb durability
Avoid traits and choices that reduce survivability