I am not sure I would put a GPS as a must have, but it is definitely a nice item to have. Electronics's seem to know just when you need it most as that is when it will fail. A chart and compass fits with the KISS principle (Keep It Simple Stupid) unlike a GPS. I have never had an issue with rain, fog, snow the only time that I have issues getting a position fix is when I am in the city. As long as the GPS can see enough of the horizon it will get a position fix, solid objects such as mountains, buildings, overpasses etc will make it more difficult to impossible to get a location fix. -Jason