Sunwalker is a gear perk that greatly cuts your movement noise during the day. It lets you sneak around outposts in daylight without waiting for nightfall.
Moving makes much less noise in daylight. Guards are less likely to hear you while you sneak between cover.
Wear the Hawkins Pool Hat or Vaquero Boots. Gear perks are fixed to the piece of clothing that carries them, so you get this one by wearing that piece, not by unlocking it in a menu.
Stalker and Travel Light reduce noise in other situations, so together they cover most of your movement.