Are we talking about stuff that can vary in size but isn't weighted? Like kiwi's or cucumbers have a fixed price each while apples or bananas have a kg price. But I don't remember seeing processed food without a kg price.

The only time I remember having difficulty comparing was different formats of toilet paper when our usual brand was out of stock... #rolls × #sheets / pack price was a bit to much for me to do in my head. Yeah, I'm not really complaining.