How to add a contact on the device only? WHenever I try and add a contact, it only gives me the option to choose which account to add it with.

How do I get the 'on this device' option?
On some devices, the "local phonebook" simply doesn't exist. But you can add it, e.g. using an app like MyLocalAccount. Here's this app's description from Google Play:


  This app does represent a local contact account. This is helpfully for devices without local contact account (f.e. Nexus series) if you don't want to sync your contacts with Google servers. These contacts can be synced then f.e. with MyPhoneExplorer to your PC.


If you wonder why MyPhoneExplorer is mentioned here: the app is from the same developer, so a well-known one. It wasn't updated for a while, but I've not yet found an alternative to it. Worth a try at least – it's free.