Ground tackle and docking tackle:
Docking or anchoring a boat without crew is difficult enough if the boat is properly equipped, and a nightmare if not properly equipped.
A good anchor windlass,
a good anchor,
a midships cleat for spring lines,
dock lines long enough to double the distance between the dock and the boat, so you can release them without having someone on the dock
larger than standard fenders—make docking single handed a bit less nerve wracking
Sail and boat handling setup:
These will vary a bit depending on the design and size of your boat...but apply to most
Autopilot and/or windvane
locking winch handles
Lazy jacks and slab reefing.
The following lines led aft to the cockpit:
Main halyard, reefing lines, topping lift, boom vang, outhaul, cunningham, boom brake line, furling drum control lines.
I don't generally include the spinnaker or genoa halyards, since many people won't use one a spinnaker single-handing, and if you have a roller-furled asym and genoa, then all you really need back in the cockpit are the sheets and the furling drum line. I also prefer a two-line reefing system, rather than a one-line reefing system.
Safety and Navigation equipment:
Pretty universal for singlehanding... unless you're on a really small lake.
Handheld VHF for boat to bridge/boat/marina comms
Good 1 liter or larger thermos for keeping coffee warm in the cockpit
Good binoculars—7x50 waterproof are about right
Waterproof chartbooks, since you'll often be using them in the cockpit singlehanding.
A good flashlight and a LED headlamp.
A comfortable automatic inflatable PFD with integrated harness and the accompanying jacklines and tether.
A good digital timer... great for setting up wake up alarms when napping during the daytime... also good to set as a reminder for doing various things....
A good radar reflector... basically this is for any boat, especially ones that have fog as a common local event.