The economy of Scandinavia in between 800 and 1000 is actually pretty complicated. So complicated, in fact, that just using the term 'economy' without further elaboration is problematic. The Vikings did not have a simple market economy, like Scandinavia has today. Instead, Scandinavian society back then (like everywhere) was highly rural. This means that the 'economy' was mostly centered around agrarian activities, that is, the farm. Yet on the other hand, trade did take place. The extent to which trade was a factor in the general economy, and the extent to which trade took place on a 'market' principle (prices determined by supply and demand) is a highly contentious issue and subject of scholarly research for at least 50 years. Some of the most authoritative works are Henry Hodges' stuff (Dark Age economics from 1986 and his updated 2000 article), or Dagfin Skre's stuff on Kaupang.

So what did Viking agrarian 'economy' look like? It was mostly concerned with land, and land could, customarily, not be sold. The rights to land you can only inherit, or steal. This means that Vikings generally have a lot of respect for big land-owners (who could also be women), who are the 'chiefs' who determine the votes of the village councils (the Thing), but they are also very wary of big warrior characters who want to meddle with this very stable, conservative, local village structure. Characters like Ragnar Lodbrok or Harald Bluetooth or Harald Fairhair. On the other hand, they need these warrior types to defend themselves against other troublemakers, so appeasing the landowners was a major task of any ambitious Viking, while at the same time trying to exploit the farmers as much as possible/was tolerated. The main system for this was the client/guest principle: a warrior or king would go around 'his' territory and be the 'guest' of his 'friends', and while he stayed at their farms he could be expected to be provided for with 'gifts'. So you see that in this model, all 'economic' exchange is embedded in all kinds of other social relations, so much so that we can not simply speak of wages or trade anymore.

So what was all this land good for? The primary measure of wealth to the average Viking Age Scandinavian was the amount of cattle he owned. Cattle, and cattle products (like cheese, milk, butter, meat, hides) could be sold, and could also be exchanged against all the other necessities of (farming) life, as well as luxury products like jewelry or wine. Normally, all craft activity also took place on an extended farmstead, which meant that a Viking farmer was largely economically autonomous. However, 'on the side' a Viking could also specialise in producing stuff, so if your farm was located near a swamp you could get bog ore for iron, and if you had lots of sheep you could produce more cloth for sale. Later on and towards the Medieval period, there is an increasing specialisation along the North Atlantic coast in preserved fish production for trade with Europe, inland Sweden had iron mines, Southern Norway exported soapstone products, and Northern Scandinavia expensive furs.

So, now that we have established the framework of Viking economics, what actually made exchange between all these products possible? Viking trade was mostly conducted through silver, which was exchanged by weight. By far most of this silver came from the east, particularly the rich Abbasid silver mines of Central Asia. Before the Viking period, smaller silver coins were also used but these were mainly from Western Europe. What mattered to Vikings was not the number of coins, but purely their weight in silver. We also have lots of silver bars or silver jewelry with little bits cut off, for example.

Viking looting activities in Western Europe were thus primarily a 'shortcut' in the economic system. Back in Scandinavia, Vikings would melt and cut up their looted silver and exchange it for mead and wenches, so to say, while selling their other stuff for more silver. So for a warrior chief, rather than a farmer, the most important was his access to a steady supply of silver with which to reward his followers so that he could acquire more silver to get more followers. This spiral of violence and wealth is not unlike what you see in modern organised crime, such as the drug trade. And like in modern crime, this type of silver economy was highly unstable and subject to inflation. The silver finds of the Great Heathen Army, for example, are very large. We also see that this type of silver economy leads to a group of men who are reliant on more and more loot, without the ability to start a farm as a way out into a more stable way of life. The Army, for example, continues to wander throughout England, gets split up, and eventually is defeated. It also means that Viking raids continue, and escalate, over time until someone manages to control these silver-addicted youths and makes them do something productive, like crusading against the Wends, at the start of the Medieval period.