shopping cart logic also applies to buying fairtrade coffee or chocolate or clothes, no one will force you to be a good person and you gain jackshit from it as a lone operator.
The shopping cart one is better because it's literally just barely more time / effort. Fair trade stuff can be expensive compared to their counterpart. People in rougher financial situations really can't make that choice every time.
I'd wager there are daily goods that have far more exploitation than most people would be comfortable with.
But you are right in some cases things aren't necessities and could probably be limited or cut out. That being said, there's a morale / mental component too. For example, you don't need that chocolate birthday cake for your sibling, parent, child, etc., but it is still is considered very important. If it wasn't there, it could be considered a huge blow and/or insulting.