With us we have some paperwork to do, takes about 30 min or so.
then one of us will go and check on the pax, point out where the cocktails are (it's self serve)
Get all the charts and App plates put away and out of the day book left by whoever flew the airplane before.
Plus we discuss things like, I bet the next freq will be xxx.x or get the Wx at destination, more paperwork.. there is always plenty to do..
If we are empty, then either the Capt or I will go back and clean up the cabin, saves time when we get home...
Then if it's real long, and you are the PNF... grab a book.
For us 4hrs is a long flight.
Oh I forgot drink coffee.. (we use starbucks)