Great question! We are all so different, yet have this flying thing in common..I've often wondered the same thing myself.
Personally: Dynamite gifts at no cost to me, to my daughter, nieces and nephews, and sisters-in-law. Trips to everywhere. "Uncle Harry" can DO NO WRONG in my family!
Also, banking the miles so my wife and I can use them when I get off the road. Enough FF miles to last 10 years, plus Marriott points for Alaskan cruises for two and inclusive RT tickets, rental car and free 5-7 night stays at Marriott resort properties.
Of course, the above has to wait until I have time to use them. Something to do in my dottage. One day soon...
Oh...P.S. and OMNI...have some of the miles/points reserved for convincing some young dude that being in the Nechetsky family would not be all that bad..have young, tall, attractive, professional (RN, BSN nurse) daughter-- mother and father would very much like to be grandparents sometime in the coming millenium...we do bribes and have no shame!!!