My GPS has a "Track Back" function which can reverse your recent track and show it as a route for you to follow. Needs careful setup and a bit of practice before you rely on it though. It will join the logged points with straight lines so if your logging interval is too long it may miss out some twists and turns, which might be ok on an obvious trail but maybe not if you've been off trail through a tight wooded area and try to retrace your steps. Easily fixed by shortening the interval, so long as you do it before hand!

And make sure you have enough memory for the track log so it doesn't run out and lose some of the route.
In fact, relying on it may be a bit risky anyway. Gizmos can always break down, or run out of power if they're on batteries, or lose the signal under tree cover, so it's best to always have a fall-back plan. I have a track log from my paraglider where for a brief period I travelled at over 2000mph to a point 60 miles away from where I'd been the second before.

Try back-tracking that one...
The Google Earth thing you could do on a mobile phone right now, if it has GPS built in and can get a decent signal. My phone happily runs it but there would be limitations and I'm not sure I'd want the phone tied to the handlebars, vibrated about and covered in mud! At least the GPS is water resistant.