In most modern video games - RPGs in particular - the principle of Money for Nothing strongly applies, to the extent that it's not rare to end some games with a cashflow in six or more digits. And several of these games depict money as collectible gold pieces. Tie these together and you have the Wallet of Holding, where a quantity of gold which would in reality amount to several tons (five million 24kt gold coins the size of the British fivepence piece would be over 41,000 kilos) and take up a colossal amount of space (the same amount would cover a football pitch) tucks up nice and neatly into a - completely disconnected part of the inventory where money takes up no space or weight.