Jur:
Cable ties for securing the load!
Not something I would trust... I suppose it's nothing to bring along a whole load of spare ones... but there are good ones and bad ones.
Julian:
There is very little load on the cable ties, in fact the assembly will sit on the stopped bike with none! The ties just stop the assembly bouncing off
The cable ties broke!
(Testing with full load through 10cm deep potholes.)