Some must have items, and why:
1. SOS automatically [and manually] inflating life vests, USCG approved. Why? Because they are the only life vests passengers will wear and never take off. Actually the problem is they are so comfortable, folks will leave your boat and drive home with them still on.
2 Two anchors are required, one front, one rear to set a boat's position when current and wind conflict to destabilize an anchored position. The two anchors together should b e heavy enough to hold the boat in the heaviest wind you never expect to be in. By this I mean in really heavy winds, both anchors will be placed together and both anchor rodes will be tied to the bow.
3. Anchor rode [rope] three or four times the maximum depth in which you will anchor. Any less and a modest wind or current will cause the boat to drag the anchors.
4. A boat hook. These make docking and departing simple and safe. For example, when you idle up to a dock, some passengers will naturally want to help. Don't let them. Ask one person sitting on the side near the dock to stay seated and hold the boat side to the dock with the boat hook, while you secure bow and stern lines.
A huge side benefit of a boat hook is best described by the following story. Most of my boating is on a spring creek in northern California. One summer day cruising down the river my wife said, "Bob, there is a snake under your seat." I am not a fan of snakes, and looked for a soft bank or tule patch to run the boat into, so I could run like hell. No spot to ground the boat was nearby so I anchored in mid-river, and picked up the boat hook, that has an end that looks like a snake handling tool.
At that point the snake decided to move from under the driver's seat to under the passenger seat. This is a small bass boat with only a couple of inches clearance between the seats the the structure on which they rest.
I put the boat hook under what I hoped to be the middle of the snake, lifted him gently and put him into the water, where he swam away with great dignity--all five feet of him!