1. Food - something he likes to eat, obviously. If you're desperate enough, candy works really well! I try to stick to chocolate if I have to choose a candy (I'm biased). Try healthier options like yogurt, raisins or his favourite fruit.
2. Toys - keep some new toys handy for emergencies like these. Or, show him an old toy he hasn't played with for a while.
3. Go outside (if he's fussing in the house)- a breath of fresh air will do everybody some good.
4. Bubble bath - I don't know what's with kids and bubbles, but they just love 'em!
5. Make silly faces - yes, transform yourself into a clown, make silly faces accompanied with sillier sounds and turn tears into laughter. Practice makes perfect.
6. The Idiot Box - no matter how idiotic it is, it does provide an option.
Remember - Distraction, Distraction, Distraction!