As you know, the Parkinson’s law states that (wikipedia):

work expands so as to fill the time available for its completion.

Knowing that this law can be generalized in “The demand upon a resource always expands to match the supply of the resource” (wikipedia), I’ve created a ‘spatial’ version after a long week end holiday in my home town:

stuff inside a bag increases so as to fill the space available

And I’ve added the first corollary:

no matter how full a bag is, coming back from holidays it will be able to contain something more (especially true in case of useless souvenirs)

This last corollary, violates the impenetrability principles: two bodies cannot occupy the same space at the same time 🙂