Recommend avoiding wax paper.  It would work but might transfer some wax to the epoxied surface and cause trouble later.  I've used plastic page protectors, Saran Wrap, and clear packing tape to good effect.

I've had just the opposite experience, actually.  Thin plastic stuck strongly enough to tear when I tried to peel it later, and waxed paper worked just fine.  In either case, a bit of sanding should clean off residue/adhered plastic, so I think either can be made to work.

This is something that I do alot in my shop. My prefered packing tape is scotch 375 o. For bending jigs and it last a long time. One of my jigs is going on 10 years. 6 mil black or clear Plastic sheets works good. Useing  thin plastic sheets can cause trouble because its so fragile when you pull it off. I use waxpaper under joints like scarfs which will be cleaned and sanded after but  it will contaminate the resin surface. Wax paper has a smooth side and a rough side. If you glue against the rough side  the resin will stick and you will have a mess to clean up. For complicated molds I sand the mold to 220 grit, spray on 4 coats of shellac. then wax with tree wax or min wax (4 coats ) The important thing is to not leave your resin cure to long , 12 hours or less then get in out of the mold or off the plastic. If you leave it for a week or more it will be stuck !!!!