When I lived in UK, I used to buy soaps, shampoos, papers, disposable kitchen goods like freezer bags from pound shops (e.g. Poundland and 99p Shop) or discount sellers (e.g. LIDL and ALDI).
In Piraeus no such thing exists and home goods like soaps are bloody expensive in supermarkets, like double or triple the prices I used to pay in UK (according to the current currency exchange rate).
But I found an alternative: Brolias in Nikitas Street.
Not always quite as cheap as in UK, but the prices here are very competitive. If you have the same problem as mine, I recommend you to try this shop (but always check the price: not everything is the cheapest).
Click this to get the map.