I hit on this idea while having a discussion about self-tinting glass. The idea started as slikscreening controls and the appropriate (transparent) electronics on the glass (e.g. a [+] and [-]) to control such windows, thereby making each a self-controlled unit.
Now extend the idea: suppose your
car windows had a small, thin interactive control panel, based on black and white LCD, bluetooth and the same transparent electronics hooking back to a computer unit. You would use a ribbon interface to allow the whole assembly to slide up and down with the window.
How it would work is this: If you pulled up to a drive-through ATM, the system would bluetooth the ATM, which would send back interface specs based on XUL or something, and display this on your window. You'ld punch the PIN in on the window, and the system encrypts and bluetooths it back, etc. The interface would be different for fast-food drive throughs, movies, road-tax top-ups, parking meters, etc.
(em.. yes, you'ld still have to open the window to get the goods, but this would be a good thing, esp in winter, when you don't have to freeze your fingertips fumbling with some controls that can't handle your mitten clad digits)