The Energy Pack (Barrel) is one of Steve's Energy Packs available to him. Its in-game description reads : "Improved Energy Pack. Has more capacity." The Energy Pack (Barrel) is the next step up after the initial Energy Pack, having 120 Energy Points instead of 80, allowing Steve to take more damage. The good thing is that it can be invented during the Photography/Make tutorial giving you less trouble to run out of fuel. If you don't make it at Chapter 1, you'll able to buy it from Cedric later in the game.