Begin by putting yourself in a positive frame of mind. You are likely to experience higher than normal levels of stress and knowing this beforehand will give you the ability to be prepared mentally and physically. You will be the anchorperson and foundation, and with your steady hand will guide your team through the stressful events. Be a reassuring and active force throughout the whole process.
It is impossible to prepare for every contingency, but planning for the known is a must. Add time or extra room to the schedule for the unknowns. When you encounter an unexpected event your schedule should not be put off by much if you have built in some leeway. It will provide that buffer that gives you and your team the ability to deal with the unknowns and keep rolling with the change process.