Truthfully? Mostly water.... filtered water (I have a filtration system on my water supply) or Penta water.
Potatey also drinks Apple Juice - Stop & Shop's (yes, a *local* grocery store chain) Nature's Promise Organic Apple Juice (no calcium added, no vit C added - my boys DO NOT tolerate anything that has calcium added - they go kooky)
Salamander drinks the Simply brand juices - Lemonade, Limeade, and Orange Juice (again, no Calcium added); he gets these diluted with Penta water.
My boys do not really drink milk. And no, they are not calcium deficient. They both take vit D, vit K and chamomile supplements. And together with the calcium they take in from their food (think leafy green veggies), we are doing just ducky in the calcium department.
We do use almond milk or hazelnut milk for cereal, baking and pancake batter.