At one time, I too fell for the "trade goods" myth. Generally, the concept
of casual trading with the natives has, long since, run it's course (unless you want to be a professional 'smuggler').
Give-aways are always appreciated (by less affluent locals), but don't expect to trade
caps, T's, lighters (etc) for bananas, or anything beyond a little good will.
Notwithstanding, I have traded gasoline for fish
You might actually have more luck trading goods & services with other cruisers.