You can easily manage non-inventory products (Pole or Helmet only) in Ski Rental.
1st, you have to select the PACKAGE as non-inventory item: see https://tinyurl.com/yunpwcap. If you don't select a different item, we think it is a Ski and needs a DIN.
You MUST click Skip Inventory in the Package Settings: see https://tinyurl.com/yksnolre
Here is how they behave in the system: video HERE.