Are the batteries accessable and do you have the tools to quickly disconnect them in case of an electrical short/fire. If disconnection is not an option, just pour baking soda in them
Actually DO a VHF radio check. I was able to receive with great clarity with mine when I bought the boat. Couldn't transmit at all. I also like to take a handheld VHF with me on trips like that.
Got some spare shackles/carabiners and some line or webbing that you can use to improvise jacklines/teathers?
+1 on stuffing box. Run the engine in gear at the dock if possible and check for dripage after.
inspect throttle and gear linkages.
Inspect diesel fuel filter bowl. (looking in diesel tank through insepection port would be much better) If it sat and they cruised inland and you go coastal with bad fuel you may get filter clogging from contamination.
Manual bilge pump would be nice....