The one essential if you want to use public charging stations is a
charge cable.
The one that comes with the car only fits a domestic square pin 13A socket. (I'm assuming UK here).
A small number of public charging stations do use these, but most require you to have a female type 1 plug (JV1772) [plugs into car] to a male type 2 (Mennekes) plug [plugs into the charging station] cable of your own.
About £300 from Mitsubishi or £80 from the likes of EVconnectors.com
You will find discussion elsewhere on this forum about the pros and cons of the variations available.
Rapid charge stations as found at motorway service stations and IKEA have a tethered cable which plugs straight into your car [CHAdeMO] - so no cable required to use these.
Other accessories will probably depend on individual requirements.
We bought
roof bars. (already used to carry extension ladders and an old up and over garage door! No doubt Christmas tree will be next.
)
Just ordered
rubber mats from Mitsu today. Only carpet mats were available when we bought our PHEV.
The best I have seen are the ones on our Toyota Auris Hybrid which have a lip all round. Brilliant. I doubt Mitsu ones will be like this. Even our Land Rover ones for the departed Freelander didn't have a lip.
Oh, also our first purchase was a
load-space rubber mat for the rear.
Essential for the winter snow if you get any. The floor in the back of the PHEV as you know is slightly raised with gulleys round the edge, ideal for trapping melted snow!
Again if you search this forum you will find plenty of discussion on all of these, e.g. official Mitsu accessories (Usually the most expensive) versus non-Mitsu