I'm going to start asking more often. I have finally gotten a bag... and that was by not being prepared. In the past I've carried one of my hand-made bags with me into banks on road trips in case they have lots of coins... now I don't carry it anymore and if they have too many to carry out they offer me a bag (or at least they have this time).
I think I'll also start asking for bags at banks I'm at often, they are good to have around.