At the office we often use 8.5 x 11″ Avery label sheets. After I’ve used up all the labels on the page, I save the sheet to use as a protective layer when pressing my collages.
I peel off the leftover sticky label borders and throw it away. I’m left with a sheet of paper that is shiny on one side. This shiny side is a “non-stick” surface.
I lay my glue-damp collage down on a sturdy, flat surface, face up; then I lay one or more empty label sheets, shiny-side down, to cover the collage. Then my pressing board, and then the weights.
If I think the glue is going to seep out over the edges of the collage, then I will cover the surface of my table with sheets of the label paper, shiny side up, before I lay my collage down.
You can use a sheet three or four times before it wears out and starts to stick to your collage.