Eating food will heal and revive your party, but you can run out of it quickly if you’re not careful. Between fights, consider teleporting back to any of the Statues of the Seven. These are large statues where you donate Amenoculus, Geoculus, and Electroculus to power up your character. They’ll revive and heal your party members when you approach them.
You can also manually heal your party by interacting with the statue and selecting “Statue’s Blessing.” Note that you can only heal so much — the amount the statue can heal will be depleted the more you do it — but it does replenish at a fairly quick rate, so don’t stress too much.