I know some (genX) people who discovered a neat trick to dislodge all the contents of a vending machine. Involves at least two people and a 2x4. I wouldn't call what is done "shaking" per se, but you can be sure when the vending machine gets set back down, it feels mighty shaken up. And also empty.
Um, there were more than a few Gen X that got hurt by vending machines. We didn’t have an immunity to that.
However, a skill we did have to exploit vending machines in the pre-digital age was to learn which alternating buttons you could press rapid-fire to get two sodas instead of one.