Don't forget the money service - managing supply and providing guarantees for its value. Actually if you manage to exclude yourself from using this particular service you won't have to pay any taxes.
That's not entirely true. I'll confine my response to how things work in the US since that's where I live and it's what I know the most about.
Attempting to use an alternate medium of exchange may result in legal problems. In particular, Federal law says:
Whoever, except as authorized by law, makes or utters or passes, or attempts to utter or pass, any coins of gold or silver or other metal, or alloys of metals, intended for use as current money, whether in the resemblance of coins of the United States or of foreign countries, or of original design, shall be fined under this title or imprisoned not more than five years, or both.
That doesn't seem to exclude exchanging goods or services for precious metals or other commodities so long as they're not cast in to something resembling money. It would be difficult to make small day-to-day purchases that way.
The other problem is that income tax law in the US applies to non-monetary compensation. If I pay you 2kg of gold to work for me for a year on a software project and the IRS finds out about it, they will demand that you pay taxes on its dollar value.
