Stamping is unlikely to work.
Stamping will probably just damage the outer case of the drive. The data is on a bit of silicon which is enclosed in it's own solid plastic case soldered to the circuit board inside.
Even if you break the outer case, and the circuit board, getting access is just a matter of some soldering. Even if you did manage to snap the flash chip casing you'd need to snap the bit of silicon inside to really do the job properly, and that's hard because it's very small, and the entire flash package is a solid mass, akin to trying to break a stone by stamping on it.
I had a mobile phone run over by a landrover, and no chips or circuit boards broke. The plastic case cracked (it's not solid) and the screen broke (it's a long thin bit of glass). Everything else inside was fine, as proved by just replacing the LCD and everything worked again.
If you really want to destroy a flash drive you are better off hitting it with something solid that isn't going to cushion the blow, like a 7ib club hammer. Comparatively soft things like shoes and vehicle tyres just spread the force out too much.