Raise your hand and ask for permission to go to the rest room.
Whip out a hanky and blow your nose. Vary the pressure exerted on your nostrils and trumpet out a rendition of your favorite hymn.
Chew gum; if the sermon goes on for more than 15 minutes, start blowing bubbles.
By unobtrusively drawing your arms up into your sleeves, turn your shirt around backwards.
Try to raise one eyebrow.
Crack your knuckles.
Twiddle your thumbs.
Twiddle your neighbor's thumbs.
Wiggle your ears so that the people behind you will notice.
(found on the internet several years ago)