We saw this experiment over on Steve Spangler's Website. I knew it was one that my kiddos would flip over. You will need:
5 or 6 sharp pencils
Zip lock baggie
towel or bucket to do experiment over
Push the pencils through the baggie without pulling them back out or you will have a water spout experiment. Push the pencils all the way through the baggie to the other side. The bag will seal around the pencils and will not leak one drop.
The plastic bag is made of polymers which give it it's stretchy quality. The polymer molecules seal back around the pencil so that the bag doesn't leak.
My kids ask to do it all the time now and show their friends the "Spear It Experiment".
Go ahead and try it, I know you have everything you need!