It has even been talked in mainstream news. Supermarkets tricks are made for you to buy more than necessary. A very sad side effect of short term capitalism thinking.
Particularly if you live alone. Typically you can't buy fewer than 6 sausages in the UK, or in Germany finding anything less than a 2.5kg bag of potatoes can be tricky.
In Germany, I find that this is one of the (many) beauties of shopping at the farmer's market. If I need 3 carrots and 2 onions and 6 potatoes, that is very easy at the Samstagsmarkt. Buying sausages or meat from the butcher or the meat counter at the grocery also supports the purchase of the exact (smaller) quantities I need.
also, quality over quantity..
At Rewe or Kaufland you can usually buy loose potatoes. The price per weight is higher than for the 2.5 kg bags, but if you only need 1 kg, it's still cheaper.