We travel with some camera gear and we've registered it. We have a folder we carry with us when we travel and it also has copies of the receipts to prove it's country of purchase.

We also list every little purchase we make on the customs declaration. When my husband was travelling with his first wife they went to Hong Kong. She did not want him to know how much she spent, so she forgot to list some things. They were delayed several hours and were fined too and heavily searched. He was none to happy about it.