I'd recommend whatever you are used to because that is what your body is used to dealing with and what are are experienced in making. For me that's coffee - I like the instant stuff with milk and sugar, which real coffee drinkers despise. Tea and coffee have roughly the same amount of caffeine so that's not an issue.

The real problem for me is going to be milk. It doesn't keep well, and I've never found a milk substitute I like. When I'm camping I take bought milk in a thermos.

My main alternative in survival kits is beef stock cubes. (Oxo brand.) These are simple to use and don't need additional condiments. You do have to watch the foil packaging doesn't get pierced. I keep them in the house anyway for making stews.