Great Thread - thanks ishoot308 for starting it.
Having learned from experience which included a $60 ticket

I now keep plenty of spare bulbs for my navigation lights.
I also have have a First Aid Kit, 2 tool kits, 1 anchor, Fire Extinguisher mounted on the front of the passenger seat base (will be adding another), whistle hanging on the dash in case the electric horn fails, large sponge and bucket, throwable cushion, 100' of rope for either the throwable cushion or anchor, paddle, boat hook, 4 docking lines at 15' ea, 2 charts of Winni, towels in case someone gets wet. 2 life jackets for occupants plus and standard orange as a spare. (I only take 2 people on board due to the boats size) If I am out at night I bring a flashlight along. Most items are stored under the seats or in a net bag under the bow but all very accessable.
I always instruct my 1st time passengers on where the safety items are located and what to do or not to do when underway or docking. I prefer to place life jackets for passengers to the outboard side of their seat for easy access and if they want they can always wear them.
All this in a 14' closed bow boat. If the boat was larger I would have even more items but space is at a premium.