Movie Cliche - Money in a Case has no mass or Volume

Stallone goes to the bank to collect his $20 million dollars in CASH. Even with the banks 20% fee this leaves $16 million. Assuming he was paid with all $100 bills - the largest US bill in circulation, that amount of money would weigh over 300 lbs. and would have a volume of a couple cubic feet. In spite of this Stallone leaves the bank carrying a bag barely large enough to carry $2-3 million waving it around as if he holding a loaf of bread. To have been realistic he would have to have had a large foot locker so heavy that he would have barely been able to drag it out of the bank -- either that or many more cases of the type he had weighing 40-60 lbs each.

Just in case you might think that he got gold instead of cash. That would be even worse, since $16 million in gold weighs almost one ton.

I wonder what the technology is that causes money carried in a briefcase in a movie to have neither mass or volume? Maybe I could get a wallet using that technology so when I go shopping I can keep pulling money out of it like circus clowns out of the clown car.