As a mutation or something. I was exploring a FEMA camp and found flasks of blood. It’d be nice if there was an obvious use for them, and if maybe there was a skill where you could drain blood from animals and zombies, but might have purify it or make blood pudding out of it to get the most benefit. Maybe living animals provide more/pure blood, dead animals provide stagnant, and zombies provide putrid blood, only good for cooking. Might give a nice reason to make fencing and house animals. The blood draining could also weaken the animals you take from.
Headgear, like a safari hat, sombrero, or something would be needed to not take damage when it’s sunny, and maybe your vision would be half or better during the night to promote hunting.