Because my setting is incredibly varied, I've been advised against attempting to ask this in a single question, and have broken this up into a series. Each context will be roughly analogous to a setting in my world(s).
Imagine that you live in France during the stone age. One day, you and five friends have the ability to magically induce redox reactions at-will.
Each person can use this ability to effect a total mass of 3 tons, per day. They can control the speed of the reaction, the scale of the reaction and remove the need for any activation energy.
The goal of you and your friends is to exert economic dominance over neighboring tribes using the least amount of this power.
You and your friends are in complete agreement about this goal and the means of achieving it. Nobody will be founding new religions around you or your powers. You have no foreknowledge of history. There are no particularly important figures for you to assassinate. Your environment and tools are otherwise typical of the time and place. The power can be used on yourselves, inanimate objects, and non-human animals.
How would you do this?