What are the common mnemonic devices used to remember equipment required by 14 CFR 91.205?
For VFR Day Flights, you can use "A TOMATO FLAMES":

A - Altimeter

T - Tachometer for each engine.

O - Oil temp indicator for each engine

M - Manifold pressure gauge for each altitude engine

A - Airspeed indicator

T - Temperature gauge for each liquid cooled engine

O - Oil Pressure gauge for each engine

F - Fuel quantity gauge for each tank

L - Landing gear position lights (if retractable gear)

A - Anti-collision lights (aircraft certificated after March 11, 1996)

M - Magnetic direction indicator

E - ELT, if required by §91.207

S - Safety belts / Shoulder harnesses



For VFR Night Flights, you can use "FLAPS". This will be in addition to all the equipment required for a VFR Flight in Daylight.

F - Fuses (spare set)

L - Landing light (if for hire)

A - Anti-collision light

P - Position lights (navigation lights)

S - Source of power (such as battery)



Additionally, as @wbeard52 pointed out below, you can use "GRABCARD" as a mnemonic device to memorise the equipment required for IFR Flight. Again, these would be in addition to all the equipment required for VFR Day and Night Flight.

G - Generator/alternator

R - Radios (two way and navigational equipment
appropriate for the ground facilities to be used)

A - Altimeter (sensitive) adjustable for barometric pressure

B - Ball (slip-skid indicator, which is part of your turn coordinator)

C - Clock (shows hours minutes and seconds and installed as part of aircraft equipment)

A - Attitude indicator

R - Rate of turn indicator

D - Directional gyro (Heading indicator)