1. Hold dead (preferably) rabbit by the torso with both hands. Head up, tail down, and the belly facing you.
2. Place your thumbs just below breastbone and press up and under the ribs.
3. Work your thumbs up over the top of lungs (about as far as they'll go), and hook them towards the spine.
4. In a left-then-right motion, work thumbs downward and force entrails out the lower "vent". Its a lot like squeezing out a big tube of toothpaste. Sometimes the guts will attempt to herniate below the skin of an inner thigh and you'll have to redirect towards the nearest opening.
5. Grab any trailing viscera and pull it out. The heart and kidneys usually remain attached (bonus!). Good stew stuff.
6. Back at camp, skin and clean rabbit as usual. Flush body cavity with lots of water. I've never had a problem with ruptured internals contaminating the meat, but better safe than sorry.
This trick is great for not making much of a mess in your game vest.
Bonus tip: In warmer months, rabbits around here host hundreds of fleas. After a quick squeeze-gut, hang the carcass in a convenient tree until your done hunting. As the body cools, many of the fleas will depart for more lively pastures.