Each fall I send my deployed penpals a little color from Minnesota. I pick colored leaves off of the trees and iron them between pieces of waxed paper. The next day after the wax paper and leaves are completely dry, I put the sheets between 2 pieces of cardboard to keep the leaves flat and send them along with other stuff in care packages. All it takes on the other end is to apply some heat (most use the hot sun) and the sheets of wax paper can be peeled off to reveal the beautiful colors. Usually my guys tape or pin them up somewhere in their living quarters.
One caution though. Mention to your Marine that the microwave could be used to warm the wax paper but the timer should only be set in 8-10 second intervals. Sometimes it doesn't take much to get the paper loosened. The first time I sent leaves in care packages, one of my LCpl's put a bunch of leaves in the wax paper in the microwave but set the timer for 5 minutes and then left the room briefly. The resulting small fire inside the microwave did not go unnoticed by the Sgt. My well-meaning but non-thinking penpal never did tell me exactly what the Sgt. said or did to him. That's probably a good thing!
In the past I've also gone out and shot some pictures of the fall colors, got them printed and sent them along with the leaves.