an oldie but a goodie, we have done this numerous times before but Ebi-kun still loves it, especially good on a hot day and easier than those kits you get where the dinosaur bones are buried in plaster of Paris.
Get a plastic box, go around the house and look for random objects, this time I used a couple of dinosaur skeletons, some shells and some small stones. pop them in the box, fill with water and freeze. Depending on the size of your objects and whether the sink or float you might want to freeze them in layers. This time I just did it all in one go. This is a great idea to have in the freezer, ready to go at any 'I'm bored' moment!
I dumped the block onto an old tray and told the boys to find something to dig it out with, kept them quiet for a good chunk of time and I managed to get some work done!