Sheila King wrote about slicing a hard boiled egg to illustrate the idea of cross-sectional areas for computing a volume. I have found that an eggplant also works quite well for this. I bring a large eggplant and a sharp knife to class that I use to cut the eggplant into slices. If you do your slices carefully enough, most of them will be rather close to having a circular cross section that is almost equal on each side (the ends cause a problem, so I usually cut them off first). I give each student a slice and a ruler and ask them to approximate the volume of the slice. We then use the individual estimates to get an estimate for the volume of the eggplant. Before class I use the old "how much water is displaced" method to get another estimate for the volume. Unlike Sheila's egg, however, no one has ever volunteered to eat the eggplant when class was over.