Heat transfer is given by TdS. Work done is given by pdV. We integrated these over an entire system, getting TS and p V, respectively. Why, then, would it not be meaningful to call TS the "heat content" and pV the "work content" of the system? (Hint: Starting near absolute zero, can you think of a way for the system to end up with TS without adding any heat, orp V without doing any work?)