4-sending-custom-properties.rb

class ApplicationController < ActionController::Base
  ... 

  private

  def track_event
    mixpanel.track(event_user, event_name, event_properties)
  end

  def event_properties
    {}
  end

  ...
end

class OrdersController < ApplicationController
  ...

  private

  def event_properties
    { quantity: @order.quantity, meal_name: @order.meal.name }
  end
end