Ah yes, I forgot the compressor and the tyre puncture kit. Also, I ended up getting a type 2 charging cable (32A) as a backup. It did come in handy last weekend while we were away, but it's hard to say for sure if you'll need it. I see they're on clearance from Supercheap for $150 (which includes a carry case), which is less than some places charge for regular 1-phase. Check the sticky on charging adaptors in this subforum. I think there are also recommendations in there for good extension cables for your granny charger e.g. for holiday house or for charging at relative's places without external powerpoints.
My "regular" (non-Highland) LR came with mats. Are there whispers that the Highland won't?
Great that you can 3d print the tray inserts. I think if I put more stuff in there I would definitely look at getting some. Especially the low one in front of the cupholders is super-deep.
E: just realised I also have a first aid kit. Just a cheapie from Officeworks or somewhere (carryover from previous car). There's a nice spot in the boot where it fits, and I can easily jam in a roll of paper towel and a couple of garbage bags next to it.