I reckon that's the starting point. When you get back look what got used and what didn't. That doesn't necessarily mean you don't what didn't get used but you need think hard about why it should be taken next time. 40kg of spare parts sounds like a lot?
To me lightness is everything. It doesn't mean I still don't carry too much, but weight is what makes things break. I think keeping below GVM is a no-brainer. If you really must carry more than that a trailer is the only sensible option but it is going to limit, or at least modify, what you can do.
Of course it's easier said than done.
Cheers,
Jon

