Are visitors to Cappella Sansevero in Naples, Italy allowed to wear a small day pack inside of the building?
I don't see anything on the website
https://www.museosansevero.it/en/guidelines-for-visitors/
there are other pages of info there you may have checked out but with most museums IF you are allowed to bring in a small day pack you may be asked to wear it on your front- not back.
I'm sure I had a backpack when I went - I always have a backpack. I don't remember any issues so I'm pretty sure I wasn't even asked to check it. This was about 5 years ago in February.