I will second the dual batter charger, it is convenient, tiny and relatively speedy. I have found this camera 'needs' fewer accessories, at least for how I use it, than other systems. Yes extra batteries - I keep 3 for trips, one in the camera and two in the charger. A 12v cigarette lighter to USB-c adaptor is useful for charging on the road.
For a L-bracket I tried the RRS, it is a pain although exquisitely machined - then I discovered the Markins L-plate for Hasselblad X1D and X1Dii here:
Markins L-bracket It is spendy at $185, it does allow the storage card door to be 'easily' accessed.
I do use the cable release although with the L-bracket that can be a PITA.
If you have any H-system glass (HC or HCD) the new Hasselblad 0.8x "speed booster" for H lenses might be interesting. The XV adaptor is all manual if you have any V-System lenses.
The filter sizes of 62 (45P), 67 or 77mm is a nice optimization on Hasselblad's part. I've had good luck with the Breakthrough polarizer and ND circular filters - with end caps they pack very small into a group of 67 and 77. I've also had good luck with the 85mm Formatt-Hitech system (if I'm really low on room in the bag) otherwise the HNY-Murami 100mm magnetic system - the HNY works very well if you use grads/ND/CPL.
I continue to use my RRS BHL-55 and TVC33 tripod or if I'm short on room, the Gitzo Traveler GK2545T-82QDUS (who comes up with these product names?). The Peak Design Travel Tripod works well for the smaller lenses (not sure I'd trust it with the 135mm).
I got a set of the Fotodiox automatic macro extension tubes for the X-system - 20mm and 48mm - I've had better luck with the 20mm of the two extenders.
The 1.7x extender for the 135mm has proved more useful than I would have guessed, although you might still have to buy them together as a set - I just call it a 180mm EFOV with the 1.7x and 105mm EFOV without, both have always been favorite focal lengths of mine on full-frame and about as long as I ever shoot telephoto-wise.
A small cleaning kit, Hasselblad blower, Hasselblad lens pen and microfiber cleaning cloths (the Hasselblad blower and lens pen were part of the 4116 Field kit. Unfortunately the X-systems sensors are dust magnets.
The 45P can sometimes benefit from a lens hood - the B+W 970/62 is my favorite.
Gosh have we had a X1D, X1Dii or 907x bag thread yet? There are so many wonderful choices that have been discussed on other threads here on getDPI - my current favorite for landscape work is the WANDRD PRVKE 21L (the smaller one), which easily fits the X1Dii with L-bracket, batteries, dual charger, USB-c cable, cleaning kit, SD card wallet, 21, 45P, 90, 135+1.7, cable release and circular filters (CPL, 6-stop, 10-stop and 16-stop with end caps - a set for 67 and 77 as well as a 62-67 step up ring) and the Gitzo tripod, which seems to get more use these days.
Glenn
