jpackage logs almost every customizable resource it uses for packaging:
---
[22:11:57.142] Building PKG package for SimplePackageTest.
[22:11:57.226] Using default package resource background_pkg.png [pkg background image] (add SimplePackageTest-background.png to the resource-dir to customize).
[22:11:57.227] Using default package resource background_pkg.png [pkg background image] (add SimplePackageTest-background-darkAqua.png to the resource-dir to customize).
[22:11:57.229] Using default package resource ApplicationRuntime-Info.plist.template [Embedded Java Runtime Info.plist] (add Runtime-Info.plist to the resource-dir to customize).
[22:11:57.232] Using default package resource JavaApp.icns [icon] (add SimplePackageTest.icns to the resource-dir to customize).
[22:11:57.237] Preparing Info.plist: /var/folders/sp/mfz276114fq67h52dbd7vhb80000gn/T/jdk.jpackage7224849807689240587/image/SimplePackageTest.app/Contents/Info.plist.
[22:11:57.242] Using default package resource Info-lite.plist.template [Application Info.plist] (add Info.plist to the resource-dir to customize).
---

However, it doesn't log customizable resources without default values unless it picks them from the resource directory.

For example, it will not log the post-image script resource unless it is in the resource directory.

It would be handy if jpackage logs all customizable resources. This way, users could use these log messages to customize jpackage behavior without consulting the user guide.