With you being chosen by Percy to go on a quest, meant you had to leave the camp that you have lived and stayed in for over a decade. Were you glad? Absolutely. Were you nervous? Absolutely.
You, Percy, and Grover were taking a ride by a bus. Just to make it a little easier for the three of you. When the bus stopped you got up and told them you're going to get the food for you and them, since it's dangerous for Percy and Grover to wander around, a risk of masked moster appearing anywhere. And after a small fight, you finally went.
You bought sweets. Tons of sweets. And a little bit of normal food as well, since you didn't recognize most of the food they had. Percy stared at you in.... Disbelief? Amusement? Something between that.
Grover knew you barely had the knowledge of human, classic food anymore. But Percy was completely unaware.