Noun: batch, lot, installment, subdivision in many sports contests, etc. (Erä has many meanings, so see the sanakirja.org entry for more.)
The word erä is frequently seen in advertisements where (like in today’s example photo) it refers to batches of items a store may have on sale for a specified period of time.
Let’s translate the whole sign, ”Erä kierrätyslaukkuja -50%,” or ”Batch of recycled bags -50%.”
Kierrätys means recycling.
As a compound word, kierrätyslaukkuja here means ”recycled bags.” (It might also mean ”recycling bags,” but we know from the context that it means the former.)
Examples of erä as a modifier: erämaa (“wilderness”), erämies (“hunter, hiker”), eränkävijä (“hunter, hiker”), eräpuukko (“hunting knife”), eräopas (“wilderness guide”)