Empty three-way boxes that the film comes in.
Obviously, when just starting out, you won't have spare empty boxes.
I was unsuccessful in finding empty boxes when I started into LF, so I made my own from shoe boxes and duct tape.
Empty a new box of film in your dark bag, keeping the film in the Mylar envelopes or loading into film holders,
then replicate from that three-way box as a pattern.
Gather the kids or grand kids around the kitchen table and make it a family affair.