The essential equipment list for investigations
A notepad and pencil
The humble notepad and pencil. Document everything in detail throughout your investigation. Log data, witness statements, timings etc.
Digital voice recorders
Ensure that you use a number of voice recorders throughout a location to capture anomalous noises/EVP's etc. Preferable choose a quality recorder with an external microphone.
Thermal imaging camera
With the FLIR One thermal imaging camera attachment, viewing and recording thermal images of your location is straightforward.
The MEL meter - used to accurately measure ambient temperature and EMF levels.
The simple torch. Not for 'spirit communication'. To see where you're going. Take plenty of spare batteries too.
A simple, cheap paranormal experiment. Set down a trigger object, draw around the outline of the object onto plain paper and seal off the room or location. Return later to see if it has been moved.