I am a fan of
Emergen'C vitamin drink mix. I have been using this stuff for a few years as a supplement to my daily vitamins when I am working alot, sleeping little and especially when I am going to be cold and wet alot.
It works wonders, helps keep me healthy and provides more sustained energey than any other supplement I have tried. I can't take it within 3 hours of going to bed otherwise I won't get to sleep (I can drink a ton of coffee right up to bed time without the same problem...)
I don't leave home without it, I always have at least 2 packages per day I plan on being gone and a ready supply in my locker at work, truck kit and 14-day deployment bag.
And no, I am not affiliated with Alacer just a happy customer