The airlines usually offer a light meal, such as a fruit breakfast or mid afternoon snack. This is exactly right, as it gets your blood sugar up without being too heavy. If possible, consider a mini-wakeup routine in the airplane lav. Wash your face, brush your teeth, comb your hair. Men can shave with electric shavers in the lav or in their seat.
Women can apply makeup, put on earrings, spritz perfume and fix their hair in their seat.
Sweaty people of either sex might consider a change of shirt or blouse in the lav. Following your light meal, coffee or juice and personal fresh-up routine, psych yourself into thinking you are wide awake and ready for arrival. Forget about being really dead tired. Look at your watch and think of local time and how you usually feel around that time of day. As the aircraft approaches the destination airport, the flight attendants pass out landing cards to all passengers.