Who did Herman Toothrot say had stolen his banana picker? (Reread the memos you've found for memory assistance.)
Cannibals took it.
You need to have stolen the cannibals' bananas.
They're in the bowl of fruit at the leftmost part of the cannibals' village.
Once you've been imprisoned, you know where the banana picker is.
But the banana picker is too big to fit through the hole in the floor.
You need to take it out the door.
To do this you need to get the Cannibals on your side.
Have you talked to them before they imprison you? (Every time you go back to the leftmost side of the Village after stealing the bananas, you will be re-imprisoned.)
Try the various dialogue options.
In particular, say "Please don't eat me! I'll give you anything."
The cannibals say they want something that will please the Great Monkey.
If you offer them various items, they say they want something of "spiritual value" that the Great Monkey could use.
The Great Monkey already has everything it needs.
Maybe you should give the Cannibals something the Great Monkey already possesses.
Or something a great Monkey Head possesses.
Maybe the Great Monkey and the cannibals would like one of the idols in front of the Monkey Head.
But it has to be an idol light enough for Guybrush to carry,
Pick up the "Wimpy Little Idol."
In the cannibals' village, give the wimpy little idol to the cannibals when they try to recapture you.
The banana picker is now yours for the taking.