It can depend wildly when and where you are. The Early Medieval English mancus, for example, was a mostly-ceremonial coin with a value of 30d. Using the generic values probably established for taxation purposed in Æthelstan's c.932 Grately legal code, that 30d might get you a horse, although it might more reliably buy you about 3 sheep.

In 14th Century England, on the other hand, rather than a mancus, that gold coin might well be a Noble, introduced by Edward III in 1344. The Noble was valued at 6s 8d, or 80d, almost three times the value of the Early Medieval Coin, and yet far more widespread in use and circulation. By the 14th Century, a single gold coin, even at the Noble's higher value, was unlikely to afford you a horse; in figures researched by Christopher Dyer in Standards of Living in the Later Middle Ages, by the 13th century, even a draught horse was likely to cost you between 10s - 20s, while a good riding horse could cost you £10.

Your 80d could afford you about 10 gallons of Rhenish wine, or 50 gallons of good ale at London prices, or almost double that at Somerset prices, which just goes to show that London's always been expensive. At a spice merchant, you might be able to purchase a pound and half of pepper, or about 6oz of saffron. Sheep were a little more expensive than in the 10th century; by the 14th century, your Noble would purchase you 4 or 5 sheep, despite its much higher relative value compared to the mancus.

Your noble might get you 13 salted conger eels to eat, or about 160lb (~70kg) of cheese.

You could use your noble to pay for about 20 pairs of shoes or a dozen pairs of boots, to buy about 10 linen shirts, or between 1 to 10 yards of wool fabric depending on quality.