Bilge pumps. You’ll want them but don’t count on them to save you after you’ve make some really poor decisions. Case in point: The Bounty. Not the 1789 version, but the 2012 version. An excellent book is: “The Gathering Wind: Hurricane Sandy, the Sailing Ship Bounty, and a Courageous Rescue at Sea”
If you’ve not replaced your smoke detectors in several years, now is a good time to put that easy job at the top of the list. Especially if you are investing everything in to a project that can catch fire. Nest Protect Smoke + Carbon Monoxide Alarm https://amzn.to/36cYjHj Ring Doorbell Camera https://amzn.to/2WJM29Z
The truth about plumbing is you will make two trips for more fittings every day and you will end up with more fittings left over than you actually used.