I've grown out a ton of bag seed (found some real gems too), but for what it's worth, I've seen maybe 70/30 female to male out of maybe 30 or 40 bag seeds I've grown... If you get a male, save that pollen and you can be a pollen chucker! It's fun... Just tell people that's what it is if you give them the seeds... Also a male seed has come from pollination, so chances are you're getting a good old-school sativa or something along those lines... depending on where your bags come from.
Also a good 10 percent of your bag seeds will just be reggies, or won't grow at all... But occasionally you'll find something killer. One of the most healthy, most vigorous strains I have was a single seed out of a bag which was male. Crossed it with some known genetics and the results were killer...