Have a bag dedicated to just church that includes quiet toys. Crayons, coloring books, stuffed animals, blank paper and whatever else you can think of that will keep your children quiet. Gauge that each toy and/or activity will keep your child engaged for 10 -15 minutes, so you want to make sure that you plan your toys accordingly.
Also, include snacks that are not messy and do not require a great deal of clean-up. Crackers and Cheerios are must-haves!