Rather than a sea anchor, I'd suggest a Jordan Series Drogue. You can read about the JSD on my
blog.
I would recommend build a proper bridgedeck at the front of the cockpit on your boat if it doesn't have one. I did this on my boat, and you can read about it
here.
You should have some sort of retaining collar on the rudder stock to prevent it from lifting out of the bushing.
You should make heavy acrylic storm covers for the ports on your boat and carry a couple of pieces of 3/8" or 1/2" plywood large enough to cover a port in the case one breaks.
A decent set of tools, including what you need to maintain your rigging, engine, plumbing and electrical systems as well as emergency tools, like a small axe, a set of bolt or rigging cutters, a small (3-5 lb.) sledge with drift punch for punching out clevis pins, etc.
Making the forward bulkhead of your boat a water-tight bulkhead in case of collision is probably a good idea. I haven't done this, but my boat has multiple hulls and each is separated into multiple water-tight compartments—and it doesn't have a heavy keel to pull it under.
Making sure that all the stowage compartments, especially ones that contain heavy items like the anchor, batteries, etc. can be dogged shut is a good idea. IIRC, Ken Barnes aborted his circumnavigation in good part due to the 14 batteries he had aboard not being properly secured, and in a knockdown, they bounced around the cabin and broke a hatch and a few other things.
As John Vigor would say—THINK INVERTED... what would happen if the boat was upside down and where would things end up.
Having properly sized wooden bungs
(softwood, with a hole drilled through the fat end, with a lanyard through the hole and stored in a sealed plastic bag) next to each through-hull is a good idea. Having a collision mat and some thin plywood and underwater setting repair epoxy are also a good idea.
Jacklines, harness and tether, as well as some decent hardpoints in the cockpit, on the foredeck and at the mast, for you to clip into are a good idea.
When singlehanding—you have to stay on the boat.
A good ditch bag with emergency water, a solar still, e-rations, a handheld VHF with extra batteries, signaling flares, mirror, etc., is a good idea.
Adding a proper first aid kit, with strong pain medication, silver-based burn creme, and other advanced medical gear and learning how to use it all is a very good idea.
I hope this helps.
