Gas cap installed, unleaded fuel nozzle restrictor ( the smaller hole with the metal flap under the cap), egr, smog pump, catalyst, evap (charcoal) canister, o2 sensor, pcv valve, and thermostatic air cleaner ( the older tube that hooked the air cleaner snorkle to the exhaust heat shield), plus any related parts for the above systems such as solenoids or vacuum hoses if applicable (some cars don't have egr or air pump systems for example. We have to compare what's listed on the emissions sticker under the hood or in our repair manual to determine what's needed.
That's just the visual emissions part, the safety part includes tire tread depth all lights, wipers, steering and braking system, park brake, horn, etc.
Edit: mirrors, exhaust system also part of safety. You got to have a muffler (turbo is considered a muffler) and no leaks.