client.js

Meteor.subscribe(
  'server_sessions',
  amplify.store('session'), // Read from local storage / cookies
  function() {    
    // The server returns only one record, so findOne will return that record
    serverSession = new Meteor.Collection('server_sessions').findOne();
    // Stores into client session all data contained in server session;
    // supports reactivity when server changes the serverSession
    Session.set('serverSession', serverSession);
    // Stores the server session id into local storage / cookies
    amplify.store('session', serverSession._id);
  }
);

server.js

// Do not have this in a model.js file, its scope should be server only
ServerSessions = new Meteor.Collection('server_sessions');

Meteor.publish('server_sessions', function(id) {
  var created = new Date().getTime();

  // If no id is passed we create a new session
  if(!id) {    
    id = ServerSessions.insert({created: created});
  }
  
  // Load the session
  var serverSession = ServerSessions.find(id);

  // If no session is loaded, creates a new one;
  // id no longer valid
  if(serverSession.count() === 0) {
    id = ServerSessions.insert({created: created});
    serverSession = ServerSessions.find(id);
  }

  return serverSession;
});