It depends on the product, but I would prioritize tests connected to actual customer complaints.
For trash bags:
- bottom-seal strength;
- leakage;
- puncture;
- tear propagation;
- load and drop testing.
For apparel bags:
- closure cycling;
- film blocking;
- rub and shedding;
- print adhesion;
- scanner compatibility.
For mailers:
- adhesive seal strength;
- puncture;
- abrasion;
- compression;
- label adhesion;
- real shipment trials.
A long list of laboratory tests looks impressive, but the most valuable program starts by asking: "How does this product fail in the real world?"
Then the test plan should reproduce those failures.