Crowther-Smith and a friend flew into Auckland on July 7 and drove up to Whangārei in their rented motorhome.
The next morning, both went to the Waipoua Forest then on to Opononi where they stopped and went for a walk.
Upon their return 20 to 30 minutes later, Crowther-Smith said they saw the passenger's window smashed and discovered a rock inside the motorhome.
His navy blue rucksack containing his British passport and a silver MacBook Pro 13 inch laptop was stolen.
He works as a script editor for a children's TV programme and said his laptop contained a lot of stuff he'd dearly love to get back.
Crowther-Smith said they secured the motorhome despite signs there were CCTV cameras where they parked the vehicle.
The friends planned to head north and explore Ninety Mile Beach and Cape Reinga later that day but were forced to cut their Northland holiday short and instead hire a rental car and head to Hawke's Bay and Wellington.
He was to have picked up emergency travel documents from the British High Commission in Wellington yesterday afternoon and will leave New Zealand as planned on Thursday.
It was his first visit to the country and said Northland was the place he looked forward to exploring the most.
"We were blown away by how beautiful Northland is and how lovely people are. They were so kind, generous and welcoming... we were humbled.
"It's my first holiday in a long time so it's quite hard to take. The stolen items are completely useless to anybody but they are priceless to me and I am prepared to offer a cash reward for their safe return," he said.
Kaikohe police confirmed a report has been lodged but no arrests made so far.
Any information on the stolen items can be passed on to Crimestoppers on 0800 555 111 or to Crowther-Smith on 0044 77531 90751 or robincrowthersmith@outlook.com.