I have 2 essentials in my boat I hope I'll never have to use, a pair of diving goggles and a box cutter/utility knife. I've actually been looking for some submersible lights with a headband. Found some on amazon but It sounded more like they were splash resistant. Those who have ever pulled a tuber know what I'm talking about.
I do have an assortment of pliers, flat and phillip's SD's, hex keys, small hammer that doubles as a bottle opener, etc. Hmm, I guess I should throw some marine sealant in the bag too.