Saturday meetup
Official xkcd meetups happen every Saturday afternoon at that day's normal geohash coordinates. All meetups start at 4:00pm* (local destination time). If you go at these times, you might encounter other readers of xkcd. Bring games!
When the coordinates fall within a body of water, you can rent a boat and win the Water Geohash achievement, or find a friendly hot air balloonist and go for Air Geohash. Use your imagination!
In other cases when it is unwise to attempt to access the generated coordinates, an alternate Saturday meetup can be suggested. As much fun as an expedition, with the addition of a Category:Failed - Did not attempt the coordinates.
*In some areas, 4:00pm is too close to sunset during the winter, so earlier meetups are often more appropriate. See individual graticule pages for local conventions.