To unlock the Hit the Road trophy in Far cry New Dawn, you must successfully complete all seven of the unique Expeditions on their highest Rank III difficulty.
To gain access to the Expeditions, you must first upgrade the Expeditions Center in Prosperity. Once you have access to Expeditions, you can play/replay them by selecting them from the Journal. The first Expedition is unlocked quite early in the game. To unlock the other six Expeditions, you must complete Rank I of the previous Expedition.
Each time you complete and Expedition, the difficulty level will increase by one, so you will have to play and complete each Expedition three times (Rank I > Rank II and Rank III). You can see which ones you have already completed at Rank III by the three stars displayed.
All seven of the Expeditions are similar in structure with only the location randomised. Get the package from the pink smoke signal, run to the extraction area, fight enemies until the helicopter arrives.
To make this trophy much easier on yourself, wait until late in the game to play the Rank III Expeditions. The additional health bars and added perks unlocked later in the game will make this much easier, as will using Legendary Weapons from the upgraded Workbench in Prosperity.
Before starting an Expedition, it is advisable to make sure you are fully stocked up on Medkits and grenades, and bring a Gun for Hire with you for some additional backup.