You kind of already have that. I’m pretty sure that the mass of anything in the grocery store includes the maximum amount of allowed cheap mass.

Standardised packaging sizes would just reduce wastage from inconvenient package sizes and streamline packaging operations. Remember the giant plastic clamshell packaging of 10-15 years ago? Takes up more space on the shelves, can make a small product noticable, and was annoying as hell and wasteful too.