I've drilled holes through the ridge of plastic which the handle is atached to, then tied in steel rings from the hardware store with Parachute cord.
Another option is to put them on the side boards and run a strap across them, with the strap set in between those same plastic ridges, provided the bucket has two of them.
Bottom of the gear pile is best though.
Be careful with the o-rings on the Buckets, as they will leak if you ever pinch them in the threads.
Obviously don't trust them for anything that you couldn't manage without.For instance, I love em for bread, but I always have some flour in my rocket box just in case.
We can't always agree, but we can still be civil to each other.