I keep a plastic drink cup next to the reloader to empty powder into and if I am leaving for a short period I will write the powder type on the cup and flip it over the powder tube. Something like a plastic Quik Trip or Casey's cup.
Thnis was something that isn't likely to repeat in the foreseeable future, as I only keep one type of powder. I just had this small remnant of Clays that I probably should have shot up or dumped. I will go through it and clean out any shot that may be left and load what I can with it, but then its history. If I get fancy enough to someday use more than one powder, or get into hunting and start to use a different powder for that, I will remember that episode and segregate the jugs so it will be difficult to confuse them.