Egg (for baking) -> flax egg: For the equivalent of 1 egg, mix 1 tablespoon of ground flaxseed with 3 tablespoons of room-temperature water and let it chill in the fridge for 15 minutes.
Milk -> soy milk, oat milk, rice milk, or nut (such as almond) milk: For calcium and other nutrients, you can look for a fortified one. You can also use coconut milk to make deserts creamier.
Butter -> oil: Sunflower or canola for baking, and pretty much any kind for cooking. If the consistency is wrong, you can try vegan butter.
Meat -> tofu: Tofu can work in pretty much any dish and is a good source of vegan protein, as are beans and lentils. Vegan meat substitutes also exist if you want another option, though they’re more processed.