Domestic Freight doggin stuff - typical fly to outstation and wait 6-8 hours.
Have breakfast, make phone calls, watch boob tube for small bit; CNN, CNBC, etc.  Go work out, have small lunch and/or go for a walk, go to stores, bookstores, or anything interesting, work on laptop computer- numerous projects or surf the web, possibly study work related issues, like systems, immediate action items, limitations, etc. (this is usually very good for inducing sleep), Have a power nap if I am absolutely whipped.  Go back to work.
Any kind of variations possible, if a car or reliable and easily utilized public transportation is available; opens up a lot of options.
International Freight Doggin Stuff - long legs, a day or more layover.
First Off: SLEEP!  Then any of the above domestic diversions, get together or hang around with other crewmembers-  try to plan something if anyone is interested, If some money is available and layover is in an interesting area, travel & exploring.  I on occasion go on day walks where I might walk 20+ miles,  I have a travel digital camera I bring with me on trips so that when I am out and about I can take a bunch of pix, download them to the computer and manipulate them as necessary.  
I guess I try to keep busy.