I do this too, if they don't have a bagger (especially if they have a line) I'll just start throwing stuff in a bag. What am I doing anyway besides just staring at them, might as well help them out.

However, I freaking loathe Kroger right now because they're cutting down on staff like baggers. Corporations see people like us helping out bagging and they see it as "Great! Don't need baggers anymore!" No you assholes, it's because you're trying to squeeze two jobs out of one person: cashier and bagger. Pay your employees double if you want them to do that.