I have used raw caffeine powder for extended periods as part of a homemade sports supplement.
I've been upto doses of 800mg per day.
I took it in 200mg doses along with 30mg of ephedrine and 75mg of aspirin at a maximum of 4 times per day.
High dose caffeine will keep you marching long after normal fatigue but you will pay a price for it later.
If you've got to stay alert and keep moving, I think that caffeine is perfect.
Just remember you will crash and need rest properly to restore your CNS.
You don't need scales to measure it, just buy a 0.5ml spoon, this provides 280mg of caffeine when level. I'd say use half of that.
I no longer use them for weight training, but I have kept 1000 tablets of ephedrine for when I need to get to the hills faster than zombies
Just to add a little info about stimulant use during an emergency:
"British troops used 72 million amphetamine tablets in the second world war and the RAF used so many that "Methedrine won the Battle of Britain" according to one report." (Grant, D.N.W.; Air Force, UK, 1944)