I picked up this neat Corgi constructor set last year.
You can swap the backs on these Commer vans to make a variety of commercial vehicles.
I had one as a kid and it was one of the few toys that I always kept in its box, since it was handy for storage.
My new example is missing its milkman and a bench seat that goes in the pickup body, but replacement parts are available.
The red cab has a form of fibre optic (well, okay it's just a perspex rod but it still uses total internal reflection) that gathers ambient light and makes the headlights bright!