The sentence that properly changes the original sentence to the subjunctive mood is:
"I wish that I was in charge of the cafeteria so that I could serve ice cream sundaes and cake every day."
Note: The subjunctive mood often expresses wishes, hypotheticals, or conditions contrary to fact, which is reflected in this choice. However, for grammatical correctness, "I wish that I were in charge of the cafeteria..." would be the preferred formulation.