The thermometer may read 20 degrees, but once you get moving out there your body temp will quickly rise, and the last thing you want to do is sweat. Pair lightweight gloves and a hat with a wicking base layer (synthetics unload sweat faster) and a vest or a thin, breathable (or well-vented) jacket. If the mercury truly crashes, wear a vest or midlayer inside the jacket, plus wind-blocking underwear under tights or loose-fitting pants.
Get a Grip:
If your local roads and trails become slick with ice or snow, consider crampon-like sole upgrades. Yaktrax ($30; yaktrax.com) and Microspikes ($59; kahtoola.com) slip easily over your shoes, and La Sportiva ($16; lasportiva.com) makes spikes that screw into soles.