I thought the OP asked what was required (as in legally required for flight)?
Read the regs (FAR 91.205) for required equipment for VFR and for IFR.
Also check the TCDS and equipment list for your airplane.
My equipment list came along with the factory W&B sheet,
it indicates items 1 (propeller), 102 (carb air filter), 103 (engine oil cooler), 201 (two main wheel & brake assemblies), 202 (two main wheel tires), 204 (tailwheel), 405 (flight manual), and 406 (stall warning indicator) are required. It does not actually clearly indicate which engine & flight instruments are required-- just which ones were installed.
The factory equipment list in my 1964 C150D was a bit more comprehensive--
it indicated which equipment was standard, which was optional, and which was required for flight.