I got some "Thinking Putty" for x-mas. Well, on the box it actually said "MisleÄi kit", but that's just some smart repacking in local language so it can be sold more expensively.
Anyway, I love this stuff. It bounces, it stretches, it tears, it shatters, it can glow in the dark, it can change color and it can attract magnets.
Throw it to the floor or against the wall and it will bounce (don't throw it against the ceiling as it might hit you hard in the head. Grab it with your hands and pull it apart, it will stretch for ever. Make it stick to the ceiling and watch it flow down slowly. Pull it apart real fast and it will tear. Hit it hard with a hammer and it will shatter, but be careful not to lose any bits and pieces of it. . Certain kinds glow in the dark, change color when heated and even attract magnets. My favorite tricks include making cracking noises and blowing it up like a baloon until it pops. There are endless posibilities to what you can do with this putty.