what items are available to have the ability to regain health during game
Well, there are health potions in Kithgard Brawl, and in The Trials, collecting a set of mushrooms fully heals you. Senick, any wizard, and a paladin can heal you. Senick and the paladin have Heal built in, and a wizard can use Regen the Book of Life and Drain Life from the Unholy Tome.
Also, I believe there are some items coming along that allow you to regenerate health.