Autobuy 2000

Autobuy 2000, or the Junk Shop, sells useful upgrades to your pod. Drills make you drill faster and help offset the harder soil as you get deeper. Fuel tanks increase the time you can spend away from the fuel station, Cargo bays and Engines increase your carrying capacity while the latter also increases your movement speed, Hulls increase your total health, and Radiators can reduce damage taken from lava and gas pockets.

You begin the game with "Stock" versions of the 6 types of equipment (called "Micro" for Fuel tank and Cargo bay), which has the lowest effectiveness. It is not possible to revert back to "Stock" versions once you bought the upgrade and saved. However, you can buy a lower-tier piece of equipment even if you already have a higher-tier version, replacing the latter. This generally represents a waste of cash and should be avoided.

Ancient Blueprints (Goldium Edition only) found deep underground randomly gives you upgrades that are even more powerful than the highest tier upgrades from the shop.

Priority
A fuel tank (e.g. Huge Tank) is usually the first upgrade you should buy, since the tank you start with will only last about 30 seconds of digging before running low on fuel, and the pod explodes instantly when fuel is empty.

Then, buy a drill (e.g. Goldium Drill) as your speed in digging depend strongly on it.

Cargo Bays
*Each ore takes up ~1 cu ft but more valuable ores are also heavier, so fewer can be lifted with a given engine.

Trivia

 * Autobuy 2000 has the lowest version designation number out of the 4 shops (2000). It also has the most generic name and the only one that does not indicate the type of business. Presumably all 4 shops are run autonomously without living operators.
 * Silvide Drill is the only Drill with its material not spelt exactly the same as the mineral (Silverium). It and the Goldium Drill are the only Drills that are more expensive than 1 of the namesake mineral; all higher-grade Drills are worth exactly 1 piece of the mineral.
 * Most equipment has 6 tiers of upgrades bought from Autobuy 2000. The two exceptions are Radiators, which lack the cheapest upgrade, the Cargo Bays, which lack the most expensive upgrade. This is likely because Radiators are only useful against lava and gas pockets, usually at -3000 ft., so it won't be useful in early game; the final Cargo Bay upgrade is unnecessary because by late game, the limiting factor is the Engine, as the most valuable minerals become too heavy to lift long before the Cargo Bay would be full.