Can I choose what is stored in icloud?

Click on this link to learn how to 'Set up iCloud on your iPhone, iPad, or iPod touch' --> https://support.apple.com/HT208681

See step 3 on how to select specific items to sync.

Also:

Change your iCloud feature settings [iOS and Mac] - https://support.apple.com/HT207689 - "'When you turn off an iCloud feature on a device, information stored only in iCloud for that feature is no longer available on the device. If you turn off Mail, Contacts, Calendars, Notes, Reminders, or iCloud Photos on just one device, you can still view and change your information on iCloud.com and on another device you set up for that feature."