Maxine Bridger suggested the excellent activity of having kids figure out how high a stack of paper would reach if you started with one sheet and doubled the number of sheets 50 times. She suggested that you start by telling the kids that one sheet was 1024ths of a foot(I think that was what she said) thick. I have done this activity and the kids love it - but I start by asking them how they could measure the thickness of one sheet using just a ruler. Usually they figure out that they can measure the thickness of their math book and divide by the number of pages (usually forgetting, initially, that the number of pages in the book is twice the number of sheets of paper). Then the process of getting the eventual distance into miles, looking up the distance to the moon or to the sun and so forth is great practice for figuring out what the appropriate operations are.