A quick activity that will go with just about any lesson about the Book of Mormon is making Brass Plates.
Just cover some pieces of cardboard with some foil and give your kids some toothpicks to write with.
From the trenches: I thought this would be a really fun activity but in all honesty my kids spent maybe a minute on this before declaring they were done. Maybe they were too young for this or just not in the mood. My daughter did come back to me later asking for a toothpick to write with again though. If you try it with your kids let us know how it went.