I'd never take my Silly Putty with me. But that's because I have a pound of it. A friend of mine in Mountain View used to buy 100 pound quanities of it from a chemical company and distribute it to co-workers. He even had the material spec sheets for them. At that time (4-5 years ago), it cost $10/pound in bulk.

A one pound Silly Putty ball can be a rather dangerous thing. And it could really mess up an airplane carpet!