Chemist shops often sold photographic equipment in the early 20th century- especially in small towns which couldn't support a specialist business. Given that photography meant darkrooms and darkrooms involved chemicals it was a perfect match! The fact that F&R Campbell were opticians made even more sense- snapshot cameras all had lenses after all.....
This is a packet of masks for magic lantern slides. The masks were finely cut pieces of black paper in various shapes such as square, oval, thick boarder etc. The masks were pressed against the glass magic lantern slide to focus the viewer's eyes on the most important, central part of the picture. The lantern would project these images onto a wall.
F&R Campbell were based in Feilding. They were advertising in the local paper in 1914 which would have been around the time these 'Primus' slide masks were made.