Large stock of Alkaline
batteries for your handhelds, and a couple sets of rechargeables and a
solar charger.
That said, you will be less vulnerable to nav errors if you have a
GPS chart plotter, and the
charts for it will be a lot less expensive than the minimum set of paper charts, but you will want at least large scale paper charts (and a way to keep them dry) for the trip.
Water maker; either a minimalist hand pumped version (desperado conditions) or some other, with the accompanying
electrical complexities. You will need a gallon per day per crew just to stay alive. Jerry cans would crowd you off the
boat, and a
watermaker can mean less weight.
You definitely want an AIS receiver and a
DSC vhf radio, to hail those big dark lumps in the night. AIS will give your their name and MMSI number, and a
DSC radio will hail them regardless of their frequency choices.