You pay £50 to go in. You get a trolley.
Fill
it up and go.

Goods are packaged in oversize boxes to
achieve a constant value/volume ratio.
Customers will not believe this, and will
always be seeking the non-existent
bargain.

Mathematicians,
geometers,
crystallographers and topologists will be
at an advantage in finding the optimal
packing for a set of unequal cuboids.

Special offers such as "free ketchup when
you buy a family pack of burgers" can be
accommodated by packaging the goods
in such a way that the ketchup bottle (but
nothing else) fits snugly into a recess in
the burger pack.

Let us take as a unit of cost/volume the 12-pack of toilet rolls. The volume of this is about 20 litres and it costs about £4. Therefore the packaging of everything in the store needs to be done on the basis that £1 of value takes up 5l of space in your trolley. So, [po]'s £25 bottle of single malt will occupy a volume of 125l, or a cube 0.5m long on all sides...

On the other hand, these are proper
English loo rolls, which can be used in an
emergency for bandaging an amputated
arm or swaddling a lamb born in the
windswept fields of Hilldaleshire. Not to
be confused with the unilamellar gossamer
which Americans wad into an immense ball
in order to provide adequate wipage.

Forget the constant value/volume ratio factor - I like the idea for a normal supermarket (perhaps without the high-end goods). The carts would have lids that must close.

Let us Tetris champions use our skills to our advantage.