Just do context.getFilesDir() and use a java.io.ObjectInputStream and java.io.ObjectOutputStream.
Also, with regard to "Parcelable not now serializable". This doesn't entirely make a lot of sense since Parcelable in an interface, not a class you extend.
So,
class MyClass implements Parcelable, Serializable {
}
should work just fine. Once you read and write the object to the file system, the Parcelable interface will still work. It's only an interface.
I have to admit I haven't tried it, but it's what I wrote today and I will be writing the unit test tomorrow.
Hope this helps.