Firstly we found some scrap card and a bottle top. Drew around the bottle top and cut out lots of circles.
This is the reason that toddlers shouldn't play with scissors...
We were lucky because the card we found was already gold on one side, so when we did the next step of sticking two circles together we already had a gold coin, but if you don't (and we had one that the gold was torn on) then you could cover them in tin foil like we did.
We needed something to store the coins in so I whipped up a really simple bag from some piraty fabric I had in my stash. They are basically a strip of fabric folded in half and a flap folded over at the top of each side to create a drawstring. You have to do it inside out and then sew the flaps in and up the sides (but not the flaps as you need to thread the string through there) - sorry I'm dreadful at explaining!
I think my little pirate likes his treasure anyhow.