Start by removing the flat surfaces of your produce containers. The top lid of a lettuce tub or plastic egg carton usually can be removed very easily without the need of scissors. However, the bottom of most lettuce or salad tubs is also a flat, clear surface that can be used for a second stencil. To use the bottom panel, use a sharp and sturdy pair of scissors to cut the flat bottom out of the produce container, then discard the sides.
Remove any labels from the flat plastic panels. If labels don't peel of easily, they usually scrub off very well with dish soap and hot water. Dry plastic sheets completely.
Place cutting mat on a firm work surface. Place your stencil design on the mat, then center your plastic produce sheet over the printed design. Tape in place.
Don your protective eye wear - it's just always a good idea while doing "close work" with a thin sharp blade.
Now, use your X-acto knife to carefully cut around the edges of each stencil area. (I find it's easiest to completely cut ALL stencil sections at once, before lifing the plastic and removing the small plastic cut-outs from each stencil opening.)
Once every part of the stencil has been cut, remove the tape and lift the plastic sheet from the design. Remove any remaining plastic cut-outs from the stencil openings, using the knife to tease them out if necessary.
Your stencil is now ready to use! To make your stencil last well for hundreds of uses, be sure to clean thoroughly after each use, and store flat.