You could only have one powder only in a TEOTWAWKI scenario.
Handguns would be nearly useless, so you would need a military rifle powder.
H335, AAC 2230, and WW 748 are the optimal powders for 5.56X45, 7.62X51, 5,54X39 and 7.63X39, and acceptable, although not optimal for .30-06, .243, .257 Roberts, .30-30 and other hunting calibers. Therefore, these would be the logical choices.