We carry a spare built up main in the hell hole, along with the ladder and towbar and it is still as big as my first apartment
The collapse-able towbar is a very nice piece of kit, but get it out and have a play before you get somewhere that is toooo freakin cold and you need to put it together in a rush.
Other than that we dont carry anything else other than a couple cans of oil and the squirter bottle used to get the oil in, just so the engineer does not need to carry it if we are down route.
Get a good floor runner, we have an additional light one over the entry as well to soak up the gunk from pax feet.