I can't remember if I shared this here before, but years ago I was flying a Hope Air flight VFR direct from Ottawa to Timmons, which means about 2 hours of nothing but lakes and woods over the unpopulated area of far West Quebec before rejoining roads and towns for the last hour and a half.
About an hour in, once I was well out of sight of the Ottawa River to the south (the only major geographical feature in the area), my usually-trusty portable Garmin 696 suddenly froze up and wouldn't reboot. I had a moment of discomfort, then reminded myself that—while it would take a lot of time to identify any specific little lake under me from the thousands on the map—I had already been flying in the right direction, so if I just kept held that heading for another 30-45 minutes, I'd be close enough to pick up the Earlton NDB (now decommissioned) to refine my course, then it would be easy pilotage from that point on along the Trans-Canada Highway or radio nav following VOR and NDB airways. Other options would have included following a VOR radial southwest to North Bay, adding a fuel stop, then continuing to Timmins from there, but I didn't want to inconvenience my (medical patient) passenger and their escort that much, especially since they were already nervous flying in a light piston single. I was also stuck at 3,000 ft below a cloud deck, so VOR reception wasn't going to be easy with the far-spread-out VORs around there (NDB was a better bet, because LF/MF signals hug the earth and have lower reception altitudes compared to the line-of-sight VHF VORs).
In the event, it took a while (I didn't have an autopilot back then, so had to do everything in 5 second segments while hand flying the plane), but I finally got the back off the 696 and pulled the battery, which forced it to shut down, then put it back together and it booted up normally.
This was not an emergency or even a particularly stressful time—I was VFR, I had lots of fuel, and a good, workable plan B and C etc…—but it did teach me always to be able to put my finger down on a paper chart and show where I am, no matter what other tech I have on board. These days, I have a panel-mounted GPS, aviation apps on a phone and tablet, and an autopilot, but I also believe that only a sucker (like I was) would ever assume that when you have a GPS you don't need anything else.
I've also flown through two GPS outages since then (one scheduled and one unscheduled), but they didn't cause any distress, because I always have backup plans.
