Depending upon the amount of equipment, the type, and how new it looks, you'll probably only need to carry proof of purchase in the U.S.. West-to-east travel seems not to be as big a hassle in customs as is East-to-west (as in Hong Kong to U.S).

I've traveled U.S. to Europe to Middle east and North Africa with a couple of bodies and lenses and have never been asked about my equipment. When entering People's Republic of China, however, it is a very good idea to check with the U.S. State Department as well as your local Chinese consulate regarding HOW MUCH equipment you may bring into their country. The general rule for non-journalists is that one is allowed to bring only ONE of any item into that country. Saying that you're a photojournalist to explain all of your equipment will probably cause you a lot of problems when you go to PRC. But you're not going there, so you don't need to worry about PRC.

Every country has their own regulations regarding this. I can't tell you about Poland, since I haven't been there. However, you may wish to fill out a declaration of your camera equipment with customs before you go. I have never been asked about my equipment, but it is better to be safe than sorry.

Before my first trip out of the country some 25 years ago, I went to the customs office with their form filled out listing every piece of equipment with a serial number. They checked the serial numbers on the equipment and stamped the form. This was proof I could show customs upon reentering the country that it was used and not subject to duties.

In more than 20 years, I was never once asked by customs about the origin of my equipment and I never got to show off my properly completed and stamped customs form!!!!

Don't worry about it.

Glenn