> you could buy some goods and services. Metal tools and farming implements, harnesses for horses or oxen, pots, clothes / fabrics, maybe woodwork for a house

You could buy some temporary luxuries to enjoy, or save yourself a bit of labour on something you'd normally do yourself. But you couldn't really invest in your future the way we would today - everything you depended on had to be something you could make yourself, buying an implement you couldn't maintain would be setting yourself up for trouble. Increasing your productivity with tools wasn't a huge help because you always had enough labor available to hit severely diminishing returns on the land you owned. And any object of value is always at risk of being seized by the local lord or a passing army or what have you.