The Boys anti tank rifle used large .550 calibre rounds that were supplied in five round clips (as seen here). These clips were then packaged into cloth carry bags, with two clips per bag to give a total of ten rounds. The bags or bandoliers themselves were intended to be disposable and were made of cheap cotton fabric:

A shoulder strap was provided to allow them to be slung over the body:

Due to the weight of ten Boys cartridges, this carry strap was securely sewn to the back of the bandolier:

The bandolier has a triangular top flap to secure over the clips of ammunition, two buttons being sewn onto the front for this purpose:

Beneath this is a stamp with two /|\ marks, tip to tip, inside a large ‘C’:

This is the mark to indicate that the bandolier has been surplused from Canadian military service. The clips themselves seem to be a snug fit inside the bandolier (I only have the one clip but it shows the principle):

I have also seen modern images showing the box magazine being carried in the bandolier rather than the clips- if this was there intended use I am unsure but I suspect that magazines were seen as expensive items that should remain with the gun and refilled from clips so the bandolier was just for clipped ammunition. The underside of the top flap has details of the manufacturer, as well as a date and the Canadian military acceptance mark:

These bandoliers remained in service as long as the Boys did, but when the rifle went out of service after about 1943, presumably the bandoliers did as well. Some were clearly sold onto the civilian marked as surplus as we have this example here, but quite what else you would use it for is unclear as it is small in size and poorly constructed.