I think there is a legal principle that takes all enumerations as closed sets.
You may enumerate a set as an example of a class. You might say, "animals, such as lions, tigers and bears." If you wrote that as legalese, only lions, tigers, and bears would be considered "animals" for the purpose of the chapter.
Legalese has to be really specific with respect to lists, otherwise clever lawyers can argue their way around the holes in whatever manner best benefits their client. If you're going to specify any sub-activity of the industry in question, you have to specify all of them that you with to include for the purposes of the law.
I would say that distribution includes shipment, so "packing for shipment or distribution" is unnecessarily redundant. As such, I would prefer the interpretation of "packing for shipment, or distribution". Just as you wouldn't say "lions, tigers, tigers, and bears" you would never say "shipment or distribution" as its own clause. Distribution is shipment.
So to make it unambiguous, you could use stricter redundancy aversion: "packing for shipment or shipment".
"The canning, processing, preserving, freezing, drying, marketing, storing, packing for shipment or distribution of:"
Lets group related activities based on what workers might be doing/where they might be doing it.
If the law intended to exclude truck drivers from overtime, our groups could be:
- Canning, Processing, Preserving, Freezing, Drying (processing facility?)
- Marketing (?)
- Storing, Packing for Shipment (Warehouse)
- Distribution (On the road)
Why is one sentence trying to define rules for all those groups?