title_body: Instant coffee to powdered milk ratio?
upvoted_answer: As a disclaimer, I've never done this, but here's the way I would do it if I were you:
  
  First, determine how you like your coffee when its a regular cup of joe.  Once you know how much milk you use to however much coffee, determine how much powdered milk reconstitutes to the equivalent amount of regular milk.  Then determine how much instant coffee in a glass of hot water makes a comparably sized cup of regular black coffee.  When you've done that, you should have measurements for how much instant coffee and how much powdered milk you need for one cup of coffee.  (Be sure to make a test cup!) 
  
  Then for ease of use on the trail I would scale up the amounts based on how long of a trip and how many cups of coffee you think you'll want and combine the coffee and milk powders.  Thoroughly mixed, they can be stored in a single container, and since you know how much instant coffee and how much powdered milk to use separately in a given amount of hot water, you can add those amounts to know how much of the mix to put in your cup on the trail.  
  
  I would do powder mix first, then hot water, and stir to combine/dissolve completely.