People with dairy allergies or on a casein-free diet, like many autistic children, can't drink milk. But there are alternatives.
Many people drink soy milk (like WestSoy or Silk) or almond milk (Almond Breeze). You can easily find these, even at regular supermarkets. If not, try Whole Foods or a food co-op (find a local one here).
However, soy and nuts also are common allergens, meaning many food allergy sufferers cannot turn to these options. Don't worry, there are other alternatives.
-- A good one is rice milk and Imagine Foods' drinks are common on store shelves. WestSoy also makes a rice milk. People intolerant of gluten should know that Imagine Foods' Rice Dream is made using a process that exposes it to gluten. Some people do not react to this, while others say they do.
-- Another option is Darifree, by Vance's Foods. This is potato-based -- no soy, no rice, no gluten. It's harder to find and comes in a powder. You can order it at the company's website. My younger daughter cannot have rice, so I have used Darifree in recipes.