Huck cannot reveal the secret to Mary Jane because he hid the money inside her father's coffin. When the phony 'uncles' stole the money from Mary Jane and her family, Huck felt bad for them, so he stole the money from the 'uncles' and stashed it away inside the coffin of a dead man, a day before his funeral. Obviously, he couldn't just let her know where he hid it, so had to find other ways to reveal this secret and make everyone happy.
Huck can't tell Mary Jane where he has put her stolen money because he has hidden it somewhere no one can get it -- in her uncle Peter's coffin.
To make matters worse, before he can get the money, the coffin is sealed shut. As a result, when Huck is telling Mary Jane about his plan to unmask the phony "uncles," he does not mention where he hid the stolen money.
A commemorative speech has to do with celebrating something or someone. If you want to pay tribute to someone (and there isn't a specific topic you have to talk about), you should talk about someone important to you, someone whom you love and who inspires you - it could be a family member or a friend, or someone you look up to.
r. Her remarks in Act I—about the location of Grover's Corners in the universe—articulate an important theme in the play: if the town is a microcosm, representative of the broader human community and the shared human experience, then this human experience of Grover's Corners lies at the center of a grand structure and is therefore eternal.