At every turn, there are signs that storm-ravaged cities along the East Coast are sputtering back to life despite numerous challenges. Sounds of trains grinding back to limited service. Buses hauling commuters down roads strewn with debris. And shivering people, peeking from bulky sweatshirts, waiting hours to fill their gas cans at stations. But challenges remain, including fuel and food shortages, and lack of electricity to more than 3.3 million customers in 15 states and D.C. Days after Superstorm Sandy barreled ashore Monday, survivors pleaded for basic necessities.