Typically 4000-6500 MSL on a cross country "going somewhere" in the UK. Keeps you clear of all terrain and everyone else. Depends on airspace though. Sight seeing typically, 500-1000AGL.
US: Typically 11000-12000 over desert areas and mountain passes.
Not used 02 yet. Hoping to this autumn so I can get to FL200 on some of my trips.