Changes of diapers and clothing, ointments and lovies all can be stuffed into the diaper bag the night before. Too many Sunday mornings I've remembered that the back of the car is too full of newspapers to be recycled, or that we have no gas. You can even put toys and books for the road in the car the night before, and whatever supplies you need for children who get car sick. I used to try to dress the kids myself while my husband waited, and then it struck us both as a waste of time and energy. Now if I'll choose the clothes, he'll dress the children and provide the voice of authority needed to hustle them all out the door.
Different people have different skills - take advantage of that fact.
I'm good at beginnings, he's good at endings, so he'll load the car with the things I choose the night before, and when the baby was still nursing he ran breakfast while I fed James. Think about what suits your personalities and skills best. Weather permitting, buckle children into the car as soon as they're dressed. This eliminates the chance of them wading through mud puddles or messing with food and toiletries. If you are bringing food for Trapeza, cook as much as you can the night before.