I agree cable ties are the easy option.
I always use a strap in the event of a burst holdall /case.
With my simple fabric straps I knot them.
With my snap together straps ( all originally found circulating on their own on carousels) I always loop heavy cord between the two halves.
I also tie holdall handles together with cord to reduce the risk of "handle strain"
On my return trip last week I thought my black Delsey had gone AWOL as I was left alone staring at an empty carousel.
A crew member had removed it at the other end of the belt (as it had a yellow label on it) and rather than put it back on the belt had left it lurking out of my sight.
Just as well as I was killing time awaiting family transport to arrive.