Hydrogen peroxide:

A powerful oxidizing agent, also rusts iron. I suggest this here because it is a great aid in burning fuels. Can also self-decompose on water and oxygen at high temperature when contact with platinum.

When burning, it releases normal fire things and steam (distilled).

Can burn oil on contact with it.

LH2:

Liquid hydrogen. Burns only in the presence of oxygen (both in gas and liquid, does not apply if it turns into hydrogen gas again)

Burns at very high temperature (always forming plasma).

Does not sink in any element in-game.

Chlorine:

Another oxidizing agent. Rusts all metals, excluding Gold and Platinum. Can make Broken metal and Broken electronics burn. May violently explode with coal. It can be liquefied at low temperature or high pressure. Otherwise, basically green oxygen.

Can be used to make salt. Deals damage to stickmen.

Sodium:

Similar to lithium, but does not store energy. When in contact with water, it releases hydrogen and EMBR, with a small chance of releasing a fire particle as well. When burned with chlorine, creates salt.

I know probably none of them will be included, but hey... I feel like there's more to powder toy.