I'm wanting to recycle household waste, where is PLA plastic used in packaging?

The most realistic materials to reuse for 3d printing would be PET and HIPS. PET is used for all kinds of beverage bottles, and HIPS is used in a lot of packaging.

PLA is not particularly common for product packaging. It exists, but you're not likely to regularly get enough to extrude and spool up. You're more likely to find it in already reusable products like rigid water bottles.