short shelf life of any milk liek product is always a concern
they do make most of theses in powder forms if you shop around, course again you could always mix protein powder and this and that and "make your own shake".

probably would be easier to eat a "meal replacement bar" or some sort and just carry water.............less weight and the nurtitional contents are roughtly the same

-dont forget your vitamins..........rarely mentioned, but for long term applications, they could really help one to "maintain" daily requirements.........and lessen chances for further problems, yeah i know the content of an average vit is minimal, but worst case senario, even using 1-1.5 /day would at least give you something, course im referring to body homeostasis, not food replacement by any means