I'll pitch in. Standardize on a strict set of allowed mixtures of plastics (and possibly even colors!). Not just "PP", "ABS" and so on, but exact formulas.

Also, keep the set of allowed formules small.

This will serve two purposes, first, allow plastics to be actually recycled to a greater extent. Now, plastics are very much "mystery" items.

Second, it will reduce the amount of harmful and toxic additives in plastics.

Somehow we also need to stop producing so much junk, electronics which is not durable, packing material within packing material and so on. The externalised costs of so many things are huge, we need to somehow de-externalise the costs.