Hold your noses: some big assumptions coming up!

If I can even glorify with the title of assumption my vague impression that the cereal aisle at Sainsbury's probably contains about 20% own brands, and that shelf space is proportional to sales, then Sainsbury's customers buy 750 x 5 = 3750 tonnes of cardboard cereal boxes each year.

Sainsbury's has 15.9% of the market, which I'll assume holds for the cereal market as well.  So, the UK consumption of cardboard for cereal boxes would be 23585 tonnes.

If a banknote weighs 1g, then a million dollars in $1 bills would weigh 1 tonne.

So $2 trillion in $1 bills would weigh about 85 times as much as all the breakfast cereal packets sold in the UK in one year.