It is recommended to do this in Pre-Outbreak because of hunger. Also, get the Anti-Gravity Goat mutator and the Sky Goat mutator. Begin the game, then jump and fly directly upwards with a parachute. Perform a forward or backward flip to get rid of the parachute, then continue going up. Activate the parachute again, and turn off anti-gravity. Wait one minute in the air until you get the "Hang Tight" achievement.