This homework assignment can be used on its own or during a unit on density. I have an associated activity in which students calculate the density of various liquids.
In class we use water displacement to calculate volume. At some points in the year, we have also covered enough geometry to calculate volume of geometric solids. This activity focuses of water displacement, but could easily be done with a geometric calculation.
As for weight, most students will not have access to a kitchen or postal scale accurate enough for their purposes. They could solve this problem in many ways. They may have access to a scale from a neighbor, at the supermarket, or at the post office. They could also use an object of known weight (pasta, beans, etc.).
The main idea here is for the kids to be creative in solving a problem. I am happy to have them give me densities in unusual units like pounds per tablespoon. The point is to come up with a density measurement outside of a classroom setting.
Students in 3rd and maybe 4th grade may need the help of a parent to complete this activity. That is fine. Getting students and parents working together on science at home is a goal of mine.