This is easiest achieved on Mission 1 (Tutorial). Your health is represented by the red bar, and armour by the gold bar on the bottom right, whilst blue is your stamina. For the achievement, you can lose health and armour during the level, but as long as you finish the level with a full bar of both health and armour, the achievement will unlock.

At the end of the level, you will drive past a beach where you will see a hut and 2 mercenaries around it, inside the barn is a health pack and armour. Kill the enemies, grab the health pack and armour if needed and continue to finish the level up the hill towards the shipwreck