What To Take On An Investigation

Some of these items are good if you are not the only "tool" of divination/detection. All of them are good ideas for a kit.

Flashlight
Digital/SLR Camera
Digital Voice Recorder
Notepad (Weatherproof)
Pen (felt-tip, not ballpoint)
Handheld computer
Extra batteries for everything
Tylenol (cold, damp or dusty areas can cause headaches)
Lip Balm (there is more time outside than one might think)
Hand Sanitizer (plastic containers, not foil because of time involved in removing wrapper)
Comfortable Shoes (preferably waterproof or hiking quality)
Extra Sweater (esp. in winter or after midnight)
Extra Socks (sometimes you muck through puddles, etc.)
Mittens & Gloves (mittens go over gloves in extreme cold)
Scarf (in winter)
Pendulum (or other tool(s), including (but not limited to) EMF readers, etc.)
Mini Toolkit (in case malfunction of equipment)
Tape Measure (you just never know)
High-calorie snack (replace some calories after long time)
Bottles water (2)

What Not To Take On An Investigation

Friends
Spouse/Mate
Children
Pets
Cellphone Turned On
Favourite Book

As you can see, there isn't much that you shouldn't take with you. Taking your friend, spouse, child or pet might be really fun, but it would be too distracting. While they might appreciate the gravity of the situation, there tends always to be a certain amount of whispering. Taking your favourite book to while away the long hours of equipment reading, etc. is just wrong because it sends the wrong message to the owners of the property and to anyone else for that matter.