Can the Android drawable directory contain subdirectories?

No, the resources mechanism doesn't support subfolders in the drawable directory, so yes - you need to keep that hierarchy flat.

The directory layout you showed would result in none of the images being available.

From my own experiments it seems that having a subfolder with any items in it, within the res/drawable folder, will cause the resource compiler to fail -- preventing the R.java file from being generated correctly.

The workaround I'm using (and the one Android itself seems to favor) is to essentially substitute an underscore for a forward slash, so your structure would look something like this:

sandwich_tunaOnRye.pngsandwich_hamAndSwiss.pngdrink_coldOne.pngdrink_hotTea.png

The approach requires you to be meticulous in your naming and doesn't make it much easier to wrangle the files themselves (if you decided that drinks and sandwiches should really all be "food", you'd have to do a mass rename rather than simply moving them to the directory); but your programming logic's complexity doesn't suffer too badly compared to the folder structure equivalent.

This situation sucks indeed. Android is a mixed bag of wonderful and terrible design decisions. We can only hope for the latter portion to get weeded out with all due haste :)

Actually, on Android Studio it is possible. You can have nested resources as shown here :

There is also a plugin to group resources here.

I recommend to avoid this though.