-
Depends on the device. Any that can hold music have fucktons of space. When I connect my 945 it tells me it has 7.9GB free (whether it can use all of this space for activities is another matter.)
My old 935 (which had way less memory) would hold at least 30 of my usual activities. If I was back to full run/swim/cycle routine that would be good enough for 2 weeks or so. Got to hope that GC isn't down for that long.
(It won't affect me, I copy data off the watch and store it myself and upload it to Strava separately. My "log" is a Google Docs spreadsheet that I manually enter stuff into myself.)
Wouldn't any activities be stored locally on the device and then be uploaded when they're back up and the device next syncs?