Exploring the swamp before you fight the Elder is overkill and totally unnecessary. And will most probably lead you into frustrating situations where you die to creeps from a biome that is higher tier than you. You do not need turnip stew to fight the elder.

Just get queens jam, cooked meat, carrot soup. And for equipment : troll armor and fine bow with fire arrows. And you are good to go. During the fight use the bow only and use the pillars around the altar to your advantage to shield yourself from the ranged attacks of the Elder. The pillars themselves are indestructible so take shelter whenever the Elder telegraphs a ranged attack. Also, if the Elder spawns roots next to where you are, just run away to some other place and re-position; do not try to destroy the roots. This is literally all you need.

IMO do not go to the Swamp before you fight the Elder. The risk you take by going to the Swamp too early so is totally higher than the boost you get from the turnip stew.