The economy was generally based on cattle, but for some segments of society (the warrior aristocracy), metals were more important, especially gold. The main carrier of value, besides 'prestige', were Roman gold coins. These were remade into the golden treasures we have from this period, but the weight of these objects often corresponds with a certain number of Roman solidi, suggesting that the objects themselves still carried a certain numbered value.

So, for the majority of the population, mobile wealth would have been centered around cattle that could be traded, but wealth was also fixed in land that could be owned. Because land is not easily sold, and requires a very long investment before it gives a yield, the Germanic peasantry developed fairly structured ways to fix who owned which property. Land outside of this structured field system was common, though grazing rights to certain pastures were likely communally (perhaps tribally) owned. For the majority of the population, then, there is not much of an 'economy' because most wealth never reaches a market; it is just inherited.

For warriors, on the other hand, gold is gained mostly through gift exchange, or through tributes (basically a 'gift' where the return is safety/protection, similar to modern racketeering). The term 'kleptocracy', an economy based on stealing, is not inappropriate here. Later, during the Migration period, it is quite likely that Romans make use of the 'skills' of the barbarians in extracting wealth from unruly peasants by giving them 'taxing rights' to some of their territories, but we have no suggestion that 'taxes' in the Roman sense existed in the Free Germanic world itself.

Tolls, on the other hand, are more likely to have existed, but not necessarily on a formal modern level, but rather again in this protection/racketeering sense; if you are a trader who wants to trade with the Jutes or the Chatti or the Heruls, you need to approach the local strongman/king first and ask for his protection, otherwise you can be subject to robbery. Of course, to become a 'guest' you need to offer a 'gift' of 'friendship'. Establishing reputation and authority amongst your group, and abroad, is thus very important for an ambitious barbarian.

There is a lot of reading on barbarian economies, but some good books would be Chris Wickham's 'The inheritance of Rome', Walter Goffart's 'Barbarians and Romans', or Guy Halsall's 'Worlds of Arthur', or Herwig Wolfram's 'The Roman Empire and its Germanic peoples'. Works that require a bit more background to appreciate would be Henry Hodges' 'Dark Age economics' or Peter Heather's 'Rome and the barbarians'.