It depends on the coffee and your taste. Instant coffee dissolves, well, pretty much instantly, regardless of water temperature. Powdered "creamer" takes a bit more time and effort in my experience. A coffee shake seems to work quite well. If I am mixing up a batch in advance, I might use Better Than Milk soy milk powder or keep the dry milk/coffee/sweetener mix in the freezer until the trip. One of my unfortunate discoveries was that dry milk can go rancid once exposed to air, as does fat. Instant coffee for cold consumption might also work with Nido instead of creamer, considering its higher fat content. Same advice about protecting the opened Nido applies, of course. If you like mocha, try instant coffee with cocoa mix. Add cinnamon for a Mexican twist.