No matter what the case, it's always crucial to have a set of items on you at all times.
- Batteries - and I'm not talking about just one spare battery for the camera but several batteries that are charged and ready to go. I have spare batteries for my camera's and phone in my PI go bag and the center console of my car at all times. My cell phone has a zerolemon battery in it that is 3.5x the size of the stock one, which makes the phone fat but the battery life is amazing. I can play on the phone without a charge for a couple days.
- Camera - Get a Sony Handycam off of Amazon or Best Buy with a 60x zoom on it. They are small, simple to use, and only a couple hundred bucks. Have a smartphone as a backup with a decent camera on it. Most have a standard 8 megapixel at a bare minimum. You want quality and features that are going to stabilize the picture. Nothing is more embarrassing than having a shaky video in court.
- Memory Cards - Get a handful of mini sdcards for your phone and camera. I say phone because I use my cell phone as a backup in case whatever reason I don't have a camcorder on me. My cell phone has 32gb memory standard, but I slap a 64gb stick in there just to have the ability.
- Cash - Always have a pocket full of cash. Hah, I like to make it a rule of thumb to always keep about $20 on me. If for any reason I need to follow someone into a restaurant and I sit at the bar and I need to suddenly leave. I can throw some cash and get out of there without having to wait on a check.
- Vehicle Repair Kit - Keep a can of fix a flat, some tire plugs for flat tires, and a vehicle jump battery just in case it breaks down. The average private investigator drives around much more than the common citizen so you need to be prepared for the inevitable flat tire.
- Car AC Adapter - Have an adapter to charge your batteries and to keep your laptop going. These run about $30 bucks or so and plug right into the cigarette heater port in any vehicle.
While there may be a few other items I'm missing here, I feel like these are the bare essentials. Remember that it's important to master the basics. Without the basics, you're simply setting yourself up for failure and a really upset client.