Or if you don't want river stones (I don't), then you can purchase small soapstone boot and glove dryers from Woodstock.
Boot dryers
Just scroll down the page to Soapstone Bootwarmers. The large ones work great for boots and the smaller ones work for gloves.
I have a pair of high boots (like loggers boot) that are insulated and naturally get wet (from sweat) when I work in the woods. Sometimes I'll put a large one in the bottom of the boot and a small one standing up.
I also use these for taking an extra pair of gloves to the woods with me. Put a soapstone in gloves, wrap them up and then when my hands get wet or cold, or both, I simply put the dry pair on. That warm glove surely feels great when your fingers are cold! They work great. We like them so much that we have 2 pair of each size.
We also use these things on top of the stove when cooking. The pots and pans sit on the soapstone blocks instead of directly on the stove so we don't scratch the stove top.