I always used a piece of scotch tape wrapped over the end of a piece of card stock with the sticky side facing out, or for that matter, double-sided tape.

I cut the card stock to be just a few mm less than the film can opening and about 4-5 inches long.

Holding onto the scotch tape, and pushing the card stock into the cannister and pulling the card stock gently out of the cannister always with the film leader attached.