This is going to sound stupid but look: you still have your old pokemon cards? Why i may ask? Well there has been a resurgence in the pokemon card wave and now old cards are worth bank, and i mean BANK.
Take this card for example
This card is worth $12,000 USD, 12,000 dollars. So obviously me, being the goat, decided to tell you now about the boom and after i get a fade, i'll tell you how to sell.