Walk it Off
From Halopedia, the Halo wiki
Walk it Off is an achievement in Halo: Combat Evolved Anniversary and Halo: The Master Chief Collection (with the word "It" capitalized). It is awarded for completing the campaign level The Pillar of Autumn on Legendary difficulty without picking up a Health Pack. In the original game, the achievement is worth 25 Gamerscore; in The Master Chief Collection it is only worth 10 points.
It is possible to complete this achievement along with the "Overshields are for Sissies" achievement.
Simply avoid picking up health packs. Most of the health packs on this level are on the right side of the doors, so stick to the left side of the doors. If the player accidentally picked up a health pack, reverting to the previous checkpoint will not reward the achievement. Due to close quarters of this level, grenades are very useful in both killing and drawing enemies out of cover. Throw grenades while still staying in cover. Burn through the Covenant using the plasma rifle on Sangheili and pistol on Unggoy, and one will eventually get to the end of the level. Dying does not invalidate the achievement, so it can be obtained in co-op, using the partner to respawn in the event of death.
The achievement's name is a phrase which means to endure one's injury, and is a slang used by some people when they hear others lamenting their pain. This is a reference to the fact that the player needs to abide with the wounds taken in combat through the level without healing. The phrase is also used as the name of the first chapter of the second Halo 3 campaign level, Sierra 117.