client.jsx

import Flux from './Flux.js'
import Flux from './components/App.jsx'

// Within document ready 

const payload = document.getElementById('payload');
const flux = new AppFlux();

flux.serialize(payload);

React.render(
  <FluxComponent flux={flux}>
    <App />
  </FluxComponent>,
  document.getElementById('app')
)

rails-payload.rb

# Controller

def action
  @payload = {MyStore: { data: [] }}
end

# View
<input value=<%= @payload %> type='hidden' id='payload' /> # Be sure to stringify hash