#9: There's Rising Water
You might notice that the bilge pump seems to be working overtime. Or you suddenly notice the boat feels heavy and seems to be filling with water.
Solution: Assuming you remembered to insert the transom drain plug (hey, we've all forgotten that at least once), and you didn't hit an iceberg, the most likely reason for the rising water is a burst hose - either on the engine's cooling and exhaust system, or an intake for a livewell or raw-water wash down. Shutting the engine down should stop cooling-related leaks, because most builders put some type of shutoff valve or "sea cock" next to the water intakes.
Those who carry spare hoses and clamps can make a quick change out. If you're not sufficiently prepared, you still might be able to cut and shorten a damaged-end fitting, or wrap a split section in tape to provide a get-home solution. A loose or split hose inside an outboard cowling won't sink you, but it will cause engine damage and might shut you down.
Prevention: Periodic inspection and replacement of suspicious or aged hoses and associated fittings.
Carry Onboard: Spare hose clamps, razor or serrated knife to trim split hose ends, and heat-resistant Rescue Repair Tape.