How do I convert 24 V from a car battery to 5 V @ 1A?
Murata has the OKI-78SR-5 which is a 7V-36V in, 5V/1.5A out, switching regulator. $5 in quantity 1 from Digi-Key. Put it in an IP54 or better enclosure, and you're good!
These are highly efficient (90%), and thus don't generate much heat or waste much energy.
That is, at 5V/1A out, it's wasting &lt;0.6W giving you 5W out.