You packs for your trip, including items to take back to your family, and you get it all packed into a case. Simples.
So, come the time to return, divested of all returnable items, how is it that you apparently have MORE stuff to pack, even without borrowing anything from your brother nor making any purchases?
Even after your mum insists on this strange archaic practice of "ironing" all yer rumpled clothes so it's a thin as a thin piece of thinness that could not possibly be thinner due to being at maximum flatness, either your case has shrunk in the heat, or your clothes have expanded.
My case is full, I've less stuff to pack, yet I've only managed to fit in half the stuff I brought!
I reckon that bane of my life, that damn Stamp Gnome, has decided to follow me on vacation, and instead of his usual thievery, whilst I sleep he's adding extra T-shirts and replacing me chargers with improbably longer and thicker leads, so that there is twice as much volume that no longer fits in the case!