Sufficient water before running will keep your muscles well-hydrated and allow them to contract and relax properly. Warming up any muscle before actual work will also prevent cramps.
Impacting the ground isn't likely the cause of side stitches, or else swimmers and other non-impact athletes would be free of them. They most likely have something to do with blood supply, but no one's entirely sure. That being said, you still shouldn't eat too much food too soon before running, but neither do you want to run on an empty stomach, so a small snack will suffice.