There are multiple options that you can customize your character in Redfall. Each hero has their own outfits, head accessories, and backpacks they can equip. On top of that, you can also change the skin of your weapons to reflect your personality even more.
With the exception of pre-order bonuses, every cosmetic item can be unlocked by simply playing the game. They are can be found in the world or are earned by completing quests. A few exclusive cosmetic items are included with the Pre-Order and Bite Back Edition of the game.
Outfits
Outfits seem to be exclusive to each character
Weapon Skins
Weapon Skins can be used on multiple weapon types.
More Redfall
Check out my Redfall Wiki if you want to be informed about the game.