Keep in mind that the 12 volts in a car isn’t really 12 volts. It’s usually a bit higher, varies a lot with engine speed (up to 14 or 15 volts isn’t all that uncommon), and is electrically very noisy (i.e. riddled with alternator and spark plug noise).
That’s a pretty wide range of current. Switching regulators often aren’t happy if they don’t have a minimum load of about 10 percent of their rated max on them. 0.2 happens to be 10 percent of 2 amps, but if you have a device that draws 2 amps you want your regulator to be able to handle that comfortably, so you’ll want your regulator to be sized for at least 3 or 4 amps. Some devices that use say a 200 mA wall wart don’t actually draw a constant 200 mA either. You may find it’s more like 20 mA with occasional peaks up to 200 mA.
Linear regulators do a lot better at handling minimum loads, but are much less efficient than switching regulators. You can always do the old trick of sticking a 10 percent load resistor on the output of a switcher. It’s not quite as efficient for lower current devices, but it’s going to be more efficient than a linear regulator for higher current devices.
A lot of load devices don’t need a particularly regulated voltage, as they have their own internal regulators, and some circuits just aren’t all that picky about their supply voltage. Other devices are very picky about voltage regulation, and some are also quite picky about noise as well. The more generic you make this, the more difficult you make it, since it has to output a much cleaner and better regulated supply voltage to handle all types of devices.