Wealth was a very different concept in the medieval ages. You can't begin to imagine it like we do today, where a dollar is good anywhere, and the number of dollars you own determines your 'power' in society.

You might have the most ducats in Tuscany, but the moment you crossed into the territory of some petty, rural nobility eating on wooden plates - you might be in a whole world of trouble.

So wealth wasn't really 'boullion'. Wealth, in the sense that we understand it, was tied up more in land, pedigree, kinship groups and followers. The vast majority of these followers received no more 'payment' from you, than a shirt to wear and a place to eat at your table.

In this sense, the real 'wealth' involved, would be whatever cottage industry that a lord might control, providing them with wool, mutton or other goods. He did not pay these people. They provided these goods to him for the privilege of living on his land without being killed. He might have very little use for 'gold'. Judging by the histories, absent a few prominent banking dynasties that arose in Renaissance Italy, most nobles were extremely spendthrift when it came to gold or silver. In much the same way that we are with credit cards.

What was 'real' to them, was the rich food, the armor, the horses, the followers, the livery. That's partly why royal families often amassed truly gargantuan debts with moneylenders.

Otherwise, they did what people have been doing with valuables for millenia. They locked it up in a secure place. As the medieval ages gave way to the Renaissance, the modern concepts of banking arose. Partly as a result of life becoming more urbanized in general, and partly from rulers exercising more control over financial matters in general. Money is just more useful for governments (especially when they can mint it and value it at their leisure) as opposed to dealing with goods or services that everyone knows the real value of. Like a war horse, arm ring, military service or milk cow.

tldr: In the early middle ages, 'gold coins' was vastly less important for gauging someone's true 'wealth' as opposed to their land and pedigree. It remained the case well into the 18th century (In France) that otherwise impoverished noble houses were considered much better off than even a rich merchant. There is nothing remotely like that today.