Turn on Low Battery Mode if you want your battery to last longer. Also turn off Background App Refresh to stop apps draining battery in the background. Notifications will still work.
Set AirDrop to Contacts Only, to avoid random people sending you files. In Siri settings, turn off “Learn from this app” and “Show content in search” to prevent background indexing from draining battery after each new iOS update. Also turn off Bluetooth if you don’t need it.
You can search for any of these at the top of Settings.