There are quite a few things you can do with leftover seeds. The simplest way to preserve them is to dry the seeds and save them to plant in the spring. You can also use them to infuse flavor and the perfect amount of heat into other recipes. Try steeping jalapeno pieces into a standard simple syrup for a spicy kick. You could also add them to vinegar to add a little bit of heat in your homemade salad dressings.