Do you mean something like this or this?

That's a Kübelwagen - literally 'bucket wagon', derived from the form of the seats, designed to protect the soldiers against falling out when driving sharp turns. Functionally, it was the equivalent of the Jeep, an easy to produce, low-maintenance all-terrain (despite only having a two-wheel drive with a locked differential) vehicle, based on the later popular VW-Beetle and then in development as KdF-Wagen.

It was ubiquitious, so it makes sense to use it in movies - it's also pretty iconic and continues to be a popular model with collectors, a derivative was in use with the West German army until the 1980s. Most of the other standard cars used by the Wehrmacht and the Waffen-SS were also convertible, which makes sense from a utility point of view.

The popular 'motorcycle with sidecar' was the BMW R-75, used mainly for motorcycle-infantry units and signals. An interesting fact is that the Wehrmacht made heavy use of motorcycles. Individual motorization in Germany between the wars was not so much achieved with cars, but mainly with motorcycle. Germany was a motorcycle-nation, not a car-nation as the modern stereotype goes. In fact, Germany was the country with the highest number of motorcycles per inhabitant, and the industry (with companies as Zündapp, DKW, even BMW ) was of an according size. So the Wehrmacht and Waffen-SS decided to put both the manufacturing capacities and the individual driving competence of potential recruits to use and created a comparatively large proportion of highly mobile motorcycle units (Kradschützen, Krad is short for Kraftrad, motorcycle, so 'motorcycle-infantry'). They were also heavily used for reconnaissance and signals.