React native + redux-persist: how to ignore keys (blacklist)?

As per the documentation, the blacklist parameter contains: 'keys (read: reducers) to ignore', so I am afraid it is not possible to implement the behaviour that you want. You can try and implement that functionality yourself, but I think the codebase of the package is really focused on blacklisting reducers instead of properties (see this). I am afraid that the only solution is to create a separate reducer for your non-persistent keys (in my experience it is not much of a hassle).

You can use Nested Persists for this.

import { persistStore, persistReducer } from 'redux-persist';


const rootPersistConfig = {
  key: 'root',
  storage: storage,
  blacklist: ['auth']
}

// here you can tell redux persist to ignore loginFormData from auth reducer

const authPersistConfig = {
  key: 'auth',
  storage: storage,
  blacklist: ['loginFormData']
}

// this is your global config
const rootReducer = combineReducers({
  auth: persistReducer(authPersistConfig, authReducer),
  other: otherReducer,
})

// note: for this to work, your authReducer must be inside blacklist of 
// rootPersistConfig

const myReducerConfig = {
  key: "cp",
  storage: storage,
  blacklist: ["authReducer"],
  debug: true
};

Use transforms for save separate fields, for example for username in redux-form MyForm inside state.form.MyForm:

const formName = `MyForm`

const formTransform = createTransform(
  (inboundState, key) => {
    return {
      ...inboundState,
      [formName]: {
        values: {
          username: _.get(inboundState, `${ MyForm }.values.username`)
        }
      }
    }
  },
  (outboundState, key) => {
    return outboundState
  },
  { whitelist: [`form`] }
)

persistStore(store, {
  whitelist: [
    `form`
  ],
  transforms: [
    formTransform
  ]
})