My own personal kit listed below, built up over the last 15 years or so:
1. Digital Voice Recorder (x2)
2. Rempod c/w temperature display
3. Digital EMF/Temperature multimeter (screen changes colour with temperature, so easy to monitor both at the same time)
4. IR Motion alarm (x4)
5. IR Lightboard (x2)
6. Laser Tripwire Alarm (x2)
7. Electroscope
8. Tesla Spirit Radio
9. Ultrasound Radar (Arduino project currently under test in a paranormal investigation role)
10. IR Illuminators (x 10)
11. DSLR Camera (for taking standard stills with flash)
12. Full Spectrum Camera
13. IR Night Vision Camcorder
14. EM Pump
15. Spirit Box
16. Ovilus
17. Magnetic compass
18. Thermal camera
19. Flashlight (x5!)
20. Laptop (for keeping investigation records and analyzing EVPs on-site with Cool Edit Pro)
21. 8x PoE IR Camera CCTV NVR system + tripods + monitor
22. Two-way radio (x4) + charging system
A ton of cables, batteries, notepads, pens/pencils, a first aid kit, and some other bits and bobs.
Last but not least, and most important - my thermos flask!
My wife hates me...........