This is a simple idea for a product, but it could potentially turn into an entire range of dual-purpose products.
The idea is to create a protective cigarette case like this -
This could then be folded into an ashtray when needed. An added feature would be to have it fold in a way to create a place to keep the cigarette butts and ash when folded into a cigarette case which could then be emptied at an appropriate time.
It could be made of metal, leather or a hard plastic to be able to function as both a protective casing and an ashtray.
The idea is simple enough and would just be a novelty for smokers, but it does open up a range of possibilities for creating containers that could be designed to serve a secondary purpose as well. This has been done to a certain degree with Chinese takeout boxes that can be used as plates. But the possibilities are only restricted by our creativity. We could have briefcases that turn into laptop stands or hiking backpacks that could be transformed into chairs. The idea is simply to act as inspiration for multifunctional products.