Android

Decompile an APK, search for *.firebaseio.com and try to access *.firebaseio.com/.json, there may be a DB
Decompile an APK and search for s3.*
Grep for android.permission.WRITE_EXTERNAL_STORAGE in the Manifest or calls to getExternal*
Grep for application/vnd.android.package-archive
Search encoded string, for example bytes[...]