Practical aspects: It seems to be agreed that the jar + Burning Plant idea is really difficult to be set up.
Why not separate the combustible from the activator? I will take a few concrete examples, but feel free to replace them with items from your world:
* Matches are the activators (could be a chemical product stored in glass)
* Coal is the combustible (could be an GMO)
This could help you to have a system of coins and bills or something, since the two products are used together to burn things With this principle you also ease trades (matches are lights, and it is easy to spare them, and to give change)
Market aspect:
A currency has a value, this value is based on another product: for example € with gold (If you have several countries and currencies it’s more based on the exchange rate and interest rate) So your currency should have a reference, something valuable which should not fluctuate too much.
But here you want to use a consumable as currency which means that its value will depend on the value of your chosen “valuable product” and the amount of your currency available (remaining matches in your country for example).
How do people earn these matches ? Is it an universal income ? How many matches are consumed by people per year? How many matches do you need for survive per year? How many matches are you earning each year? How much is it fluctuating during the year? (consuming/earning rate)
Those questions will help you determine your currency fluctuation, but also to determine the real impact on the market (inflation and deflation)
You can imagine that the value of coal will decrease in summer, and dramatically increase in winter. I would suggest to have durable matches to always have a stable amount of matches on the market: the amount of matches/coal should drop significantly in winter, if a match has a short lifetime then in spring there will be no resources left.
This is a real problem: if one match is worth one bread in summer, one match could equal ten breads in winter. 130
How do you really determine the value of your currency ? Keeping that in mind people will probably prefer to sell in summer and to buy in summer.
Separating the activator from the combustible (and maybe the combustive?) could introduce some new concepts: - You waste matches when failing the strike, and as matches are your daily money and the value is evolving, wasting a match in winter means losing a lot - People always want to optimize things, they will develop techniques intending to limit the waste of coal/match; - People will take risk in selling all their matches during winter and buying a lot in summer. - Poor people will buy the bare necessities of life selling there last remaining matches.
Have you read the stormlight archive by <PERSON>? There are some similarities as they use glowing spheres as main currency, meaning they use it for light as well as money. These aren’t really combustible as they are rechargeable but the Wkipage could give you ideas https://en.wikipedia.org/wiki/The_Way_of_Kings
EDIT: Hope this is better 130