This is how I get almost 3 days out of an iPhone 13 mini:

1. data safer on; certain apps blocked to use mobile internet as well.
2. battery always in low power mode; this also prevent apps from doing stuff in the background
3. wifi and LTE/5G/4G only on when I actively use my phone or cannot miss a reply I am waiting for
4. lowest brightness setting as the base in a dark room and adaptive brightness from there
5. no automatic app updates to safe on data plan and battery. updates only with wifi at home
6. download favourite music instead of streaming (apple music can do that). hear music offline. do nothing else while listening to it.