First, just pay the extra £350 and buy all the extras with your Mavic: two spare batteries, multiple battery charger, car charger, phone charger, spare props. No point going to an amazing location and taking only one battery and no chargers. There’s also a bag, but it’s useless once you have the essential travel necessities too.
Instead I got a Peli iM2100 storm case. There’s a B&W equivalent with laser cut-outs, but I prefer to do my own hole making for exactly the pieces I need. And the peli case was available unlike the B&W equivalent.
Joystick clamp: with a custom cutout peli case (and actually even with a laser cut B&W), it’s worth keeping the joysticks on the RC aligned in storage as the instructions say.
Launch pad: not a necessity but there is good reason – on take-off there’s a pause while the Mavic photographs the takeoff point; on return to home, GPS gets the Mavic most of the way home but the launch pad recognition gets it to within a few centimetres.
Landing Legs: unless you’re on a hard, dry surface you’ll need these little legs to keep the camera and gimble off the ground and away from the damp grass.
Cheap mobile: No point risking your iPhone or Samsung when a £60 Android will fit perfectly and provide a fantastic 5.5″ screen; no SIM required though if desired, this one supports 3G, and it’s £69 sibling adds 4G and LTE.
P.S. I’ve found a couple of other options worth mentioning:
For the joystick clamp, I’ve swapped to this one, which is injection molded rather than 3D printed. It’s a better design, a better finish, and cheaper.
For connecting the cheap mobiles to the RC, none of the standard adaptors supplied by DJI work. There are two choices:
Neither option is perfect, just make your own choice.