You have to at LEAST have tried doing each and every skill before using the mega skill option.
As in shooting, killing, looting, running(for stamina), etc.
It doesn't seem to work if your inside of you're base. Leave base then give it a try.
[Edited by Pfenixtx, 11/9/2013 3:14:00 PM]
As I mentioned before, yeah... Just leave your base and then try the stockpile option.