Front wishbones are a good spare if you drive like me. Though I would recommend the Medium Flex for strength (
here). Diff outdrives are a good spare, although when you limit travel and widen the car you significantly reduce any breakages.
The only other thing I have broken is the front upper transmission housing, so I switched to alloy. Then again that was a mighty crash with a post, so not sure if it really is needed as a spare.