Robert,
Generally if there’s a seat available in the cabin you’ll get that. Technically if you’re in the cockpit you’re an additional “crewmember” and as such should conduct yourself appropriately. That said most pilots don’t expect a JSer to be actively participating so as long as what you’re doing doesn’t violate any airline procedures or regs or distract the crew you can do as you like. Proper etiquette dictates you ALWAYS ask first before turning on any device.
As long as we’re on the subject take a look at this story I posted not that long ago: How NOT to get to a Major
Adam