Slice of life is about things that matter in life. It's about shifting your perspective and appreciating the small things. The supermarket is a great example. It doesn't seems exciting but it's something we do often but don't think about doing often. The term defamiliarization comes to mind (see: https://en.wikipedia.org/wiki/Defamiliarization).
I made one comment here: https://lemmy.dbzer0.com/comment/2659409
And there's a huge amount of recommendations here: https://lemmy.dbzer0.com/post/3287665