It's quite scary to find out that you've been doing 95-100kph downhill with a couple of planks strapped to your feet...
The SkiTracks app would happily log a day's skiing on a Samsung phone (can't remember the model), which says something for the battery life, processor loading, GPS power, etc. And all this with the phone stuffed in a jacket pocket.
It would work on my Hudl tablet, too, but I never had the nerve to take it out stuffed in my little MTB rucksack... Being bigger than a phone, there's more chance of the screen getting cracked due to being bent (leverage, and all that).
I was very glad of the little Decathlon Wed'ze lightweight down jacket that stuffed easily into the bottom of the MTB pack; just the right amount of insulation to cope when it got below -10.