Yes. \"Putty molds\" are an excellent thing to do with that leftover green stuff.
I have an assortment of skulls, heads, hands, chainmail and scale textures, etc. Put that bits box to work! I attach a little toothpick to the end of the stamp, add a little more green stuff to make a little stamp handle, and then trim the outside \"cutting\" edge of the stamp, so when it stamps it makes a nice clean outline. This way, you can pick off the \"oversquish\" with ease, after your stampings harden.
I also attach little balls of putty to the ends of toothpicks, for when I will need head armatures. Its nice to use a little putty core for those new heads and faces, and the toothpick is nice to hang on to while sculting.
Also, making little hearts for your boyfriend/girlfriend is a good idea. Try to sculpt in your initials and theirs, like people carve in trees. There are no greater gifts then the ones that are handmade! Super cute!