I should clarify, these are British superstitions, so there are plenty more where those came from.
I think a lot of the sixpence superstitions have their roots in the biblical thirty pieces of silver, the sixpence would be the coin to carry such superstitions as even lower income families would be familar with them. People still buy sixpences off ebay to bake into christmas puddings and sometimes christmas cakes. If you recieve the sixpence you get a years worth of luck. But if you choke on one or break a tooth, that's clearly not so lucky.
Romany families, even today, wear a lot of gold sovereign jewellery. This harks back to the need for nomadic people to carry their wealth with them for security. They do see gold as an impure metal compared to silver, I'm told.
My partner points out that placing pennies on dead people's eyes, apart from being useful to undertakers, is also to pay the Ferryman across the River Styx. He also has heard the one above,that to pick up a found coin with tails showing is unlucky.
It's seen as bad form to give someone a wallet or coin purse as a gift without at least a penny in it, or else you condemn them to poverty.
And finally, now I know why so many coins in my collection are ruined by holes:
https://en.m.wikipedia.org/wiki/Touch_piece
Edit to add: I'd really like to read the former threads on this but the links direct to page not found?