I watched a programme this evening, "Tribes" by David Attenborough (I think you'd enjoy it), in which I watched a group of Solomon Islanders make shell money.  They were the only people who made this money, which involved finding certain shells and then working them to a round and very smooth finish and drilling a hole through them; the one tribe were the only ones to make this money, but it was used widely--by many other tribes.  In the film the two uses shown were: a brides dowry, where huge chains of these small worked shells were hung up in preparation for their transfer to the brides new husband; and as a welcoming present for David Attenborough, symbolic in this case.

So I think there are two elements (maybe!) for a currency to have intrinsic value (where you'd keep it just because you wanted to, rather than "transactional", where your only plan is to replace it with something more immediately valuable):

1. Human labour producing something of obvious and basic value: just one example: gold is considered beautiful by humans; it does not tarnish and does not rot.  (Ditto the polished shells, though they may be easier to break--but there were a lot of them!  And shell is tough!)

2. A scarcity value implied by this need for humans to "work to produce the money"...hmmm...

You can't spend gold at the supermarket, but if you have a bar of it, or some coins at home, or in your pocket, you have a lot of "money"--it is still valuable, and its uses keep growing, I suppose (I'm thinking electronics, but I'm sure it has many applications.)

Don't fight forces, use them R. Buckminster Fuller.