Exercises
Whenever you are going to travel for more than an hour
you must consider what exercise that you will need. 
At home you never sit in the one place for a long time
without moving and exercising your muscles.
So why would you expect to sit in your seat on a
jet plane for 3-15 hours and not consider exercising?
I regularly flew 12-15 hour trips and ensured that I walked around the cabin a couple of times (avoiding meal service time).
Meal
serving time is not considered an appropriate time to
demand to be able to walk around the cabin. Cabin crew
have a difficult time in serving meals to hundreds of
passengers at the same time as it is, without having
to dodge "athletes" striding along the aisles.
Wait
until the meal service is over and try to walk a little
every hour or so when you are awake. After a sleep session
try and take a small walk again. If your fellow traveller
is still asleep, exercise your fingers and toes.
The pilot numbers on flights
differ depending on the length of the flight. A two
person/pilot aircraft can be flown up to about nine hours
before another pilot has to be carried for in-flight relief/rest.
Most airlines take another pilot for flights of 12
hours or longer. The reason being that there are
always two pilots on the flight deck. On long flights
extra pilots are carried to enable other pilots to take
a rest. Would you be happy to fly on a 14 hour flight
with just two pilots? Imagine how tired you would
be at the end of a 14 hour flight and have to land your
plane. Not many people go to work for 12-15 hours
at one stretch and the most important part of their work
period is at the end, the last couple of minutes. So
pilots need to be alert and, to achieve this, rest breaks are necessary.
While
I am talking about pilots, the pilot numbers on flights
differ depending on the length of the flight. A two
person/pilot aircraft can be flown up to about nine hours
before another
pilot has to be carried for in-flight relief/rest.
Most airlines take another pilot for flights of 12
hours or longer. The reason being that there are
always two pilots on the flight deck. On long flights
extra pilots are carried to enable other pilots to take
a rest. Would you be happy to fly on a 14 hour flight
with just two pilots? Imagine how tired you would
be at the end of a 14 hour flight and have to land your
plane. Not many people go to work for 12-15 hours
at one stretch and the most important part of their work
period is at the end, the last couple of minutes. So
pilots need to be alert and, to achieve this, rest breaks are necessary.
Beware
of travelling in an aeroplane without having your seatbelt
fastened. Pilots continually warn passengers that whilst
seated they should keep their seatbelts fastened. The
reason is there is no device that can detect clear
air turbulence. So when you are moving around the cabin
in-flight you do so at your own risk, so please be
careful.