Classic Stock is a Play Mode inspired by the resource system proposed by NovaSilisko and HarvestR for KSP 0.19, and which uses a new and minimal set of mine-able resources:

• Original Classic Stock resource flowchart
  As a niche mod, it enables many things that the Community Resource Pack does but with a working asteroid scanning function and without needing to provide a very lengthy resource library that usually goes over 50% unused at a given time by most players.
• New Classic Stock resource flowchart

Resources

• Atmosphere: Equivalent to IntakeAtm, it is the raw catch-all resource for intakes that don't depend on Oxygen, and for any engines that also don't need Oxygen. Prospectors that work in atmosphere and in space are able to sift all other raw resources out of this once they are present at the current celestial body.
• Blutonium: Raw radioactive material which is dug up from the ground.
• Explodium: Equivalent of Nuclear Saltwater. Do not attempt to swim in, ingest, or in any other way handle with bare skin. It is a compound of Blutonium and Water. If and when you separate them...would you drink the Water?
• Gemstones: Precious stones with all colors and internal arrangements. Their primary purpose is for funding the next great mission.
• GrayWater: Water is not actually clean as we know it by default. Drinkable, otherwise pure water nearly always must be filtered from this.
• Hexagen: The Helium-alike resource. Very plentiful at stars and gas planets. It is the standard option for fusion drive propellant, and the fuel for compatible fusion reactor power sources.
• Hydrokerbon: Raw material rich in hydrons and rich in kerbons. It converts with 100% efficiency into two propellants that are greater than and equal to LiquidFuel, and can be fissioned for Propellium.
• IntakeLqd: Equivalent to Atmosphere but for prospectors that operate only while splashed and submerged.
• Minerite: Particular common materials not found in Ore such as salts and semi-precious crystals.
• Nitronite: A powerful Nitro-bearing compound, very versatile and largely produced by microbes. It is a key component in the production of MonoPropellant and LFO, is an inefficient propellant in itself, is useful in distillers, and can be used to turn frowns upside down! It's plentiful here on Kerbin but we're not quite sure about other planets yet...
• Oxium: Pure Oxygen. Less awkward than "Oxidizer" for use in potential resource chains not involved with propellants.
• PreciousMetals: Rare, high value metals. Their primary purpose is for funding the next great mission but they can also serve very well in industrial processes.
• Propellium: Cryogenic fuel, liquid hydrons. It is best found very near stars and at gas giants.
• Rock: Can be found/treated as space dust. More abundant than Ore and the major constituent of planets. Can contain Ore. Easiest to harvest. Does not convert well but can be effective in a pinch.
• Slag: Waste product from Ore refinement, major component of Konkrete.
• Water: As you know it, pure and usable for many processes, but it is not all-present by default. In most cases it needs to be filtered from GrayWater.
• Zeonium: Crystalline and like a fine powder, contains XenonGas and possibly other noble gases. Abundance may be biased towards particularly hostile planets. It can be found in crust and in atmosphere.

Pathfinder Templates

Each template switches over to use the resources in their converters. Below is the complete list with the exception of converters created to support 3rd party mods.

Designer's Notes

Creating this resource system was an interesting challenge. If you look at the image by NovaSilisko and HarvestR, you can pull Propellium and Oxium straight from the ground, and from Eve's oceans, and they're made by splitting water. I couldn't wrap my brain around that; we know that hydrogen and oxygen form water, so how do you pull hydrogen and oxygen directly from the ground?

Sure, some compounds have hydrogen and oxygen from them, but the diagram is essentially treating Propellium as an analog to hydrogen, and Oxium as an analog for oxygen. Plus, the diagram shows how Propellium and Oxium feed directly into LiquidFuel and Oxidizer. But the other problem is that even when liquified, the density of LH2 and LOX don't match stock density for LiquidFuel and Oxidizer- both are much heavier than their real-world counterparts.

That's when it hit me: don't pull Propellium and Oxium from the ground, and to account for the mass differences, add something to the conversion process between Propellium/Oxium and LiquidFuel/Oxidizer. Hence, Minerite and Nitronite are added to the fuel mix to make up the mass difference, and you get Propellium/Oxium from GrayWater.

Eve's oceans was another tricky one, but I solved it by creating Explodium, a solution of Water and Blutonium- not unlike the solution you need for a nuclear salt water rocket! I figure Eve's oceans also have some carbon boride mixed into the ocean to inhibit neutrons, less the entire planet explode in a thermonuclear explosion. And with Explodium separating into Water/Blutonium, I can keep to the spirit of NovaSilisko's and HarvestR's vision. Plus, now I have a new fuel source for a new nuclear engine! :)