Coleman cooker and the dogs ......
Seriously though,
It depends on how extreme a lane you are intending to drive,
I havn't bothered with any extreme underbody protection as i don't drive any severe lanes in either of my landies (especially the 109),
Leave that to those with "One life,get one" stickers in the window
The most important bit is to not go alone so if you do get stuck a bit then you have help to get out of it
A couple of recovery strops,a shovel,some basic tools ...A high lift jack(and the knowledge of how to use it safely

)maps(having checked the definitave ones with your local rights of way officer),mobile phone,camera(for scenic piccies)brew gear (for having a brew in scenic locations)