The short answer
Creatine monohydrate: 5g daily. Cheap, well-researched, no need to cycle. Works on carnivore the same as any other diet.
Electrolytes: sodium, potassium, magnesium. Most 'carnivore flu' symptoms are electrolyte crashes - supplement in week one.
Vitamin D3: if you live in Cape Town and work indoors, yes. 2000 IU daily is the standard dose.
What you don't need: protein powder, BCAAs, mass gainers. You're already eating 150g+ protein per day from meat.
The supplement industry sells a lot of snake oil to carnivores. Here's the honest list.
Tier 1: Worth it for almost everyone
Creatine monohydrate (5g/day) - the most studied sports supplement in existence.
Electrolyte blend - prevents the keto flu most people feel in weeks 1-2.
Magnesium glycinate (300-400mg before bed) - sleep quality support.
Tier 2: Consider if relevant
Vitamin D3 - if you don't get 20+ minutes of midday sun, worth supplementing in winter.
Omega-3 - if you don't eat fatty fish weekly, consider algae oil.
Tier 3: Skip
Multivitamins - eat organs instead.
BCAAs - redundant when already at 2g/kg protein.
Testosterone boosters - essentially zero evidence.
Collagen supplements - bone broth gives the same amino acids at a fraction of the price.