The kids had a regular-size cup of Play-Doh for every 2-3 people. They split the play-doh and had plenty. First, we crafted rectangular prisms. Then we sliced them into 1 cm cross-sections. Students analyzed the shape of one "slice" and found its area. We decided, then, that we could simply multiply this area by the number of slices we had (it's height) to find the volume. We repeated this process for triangular prisms and cylinders. Students derived the formulas for the volumes of all three. One student informed me that "[Volume] was the easiest thing we've done all year". Good. It's easy because they really understand the formula. Great day.
Some kids discovered some other geometric properties... Hello octagon!
...And we still managed to have a little fun!