One of your most important, yet overlooked resources as a PC, are your healing surges. Healing surges in 4e D&D are the difference between life and death. Effective use of those healing surges can mean the life or death of you and your companions.
Healing surges are a new mechanic to D&D that were introduced with 4e. No longer do you heal a certain amount of hit points by resting or from relying on the Cleric to have enough healing spells or the right combination of healing potions. Now every PC is equipped with the ability to heal themselves during and after battle.