Re Leclerc and/or Auchan
I seem to recall a time when for every euro spent… one got a tiny amount added to the loyalty card… soon mounted up and gave me a free-shop at Christmas…
Still got the loyalty cards, but points don’t make many prizes nowadays… although getting even a small amount off is very welcome…
One issue that you may come across is the PIN for your carte fidélité. Mine is the last four digits of my (French) phone number.
The Pin is not an issue… remembering what it is… that is an issue 
(for me anyway… too many cards and too many pins… aaargh)
Stella, I fully appreciate the issue around remembering which PIN goes with which card. My point was, having forgotten my PIN I went into my local store to get it reset. I was asked to put my phone number into a keypad to confirm my identity (I assume) and was told that my PIN was now the last four digits of my French phone number.
that’s interesting… last time I wanted to use my Leclerc points… I went to the Staff Help desk before going into the shop itself… and they wanted my passport …
Passport is rarely with me, but my phone number is engraved on my heart 