A couple of years ago, our previous State Government hosted an "open weekend" on projects that it was sponsoring as part of a PR exercise. One of the activities that was featured was the use of a chartered cruise boat which performed a tour of all of the new sites that were along the Yarra river.
What was done was that, rather than having a tour guide explain the sites, they played a cassette which had pre-recorded commentary through the sound system as the cruise boat was at the various points of interest.
MiniDiscs can suit these kind of bus or boat tours. For example the itinerary can be varied at the last minute without having to fast-forward or rewind a cassette to suit. There is no need to worry about tape being "snarled up" in poorly-maintained sound systems.
What you need is a MiniDisc with audio commentary for each waypoint; a MiniDisc Walkman; a power adaptor which runs the MD Walkman off the vehicle's or boat's cigar lighter or accessory socket (or a mains power adaptor in case of boats equipped with a mains-level power supply); and a cassette adaptor which slots into the vehicle's or boat's cassette player and connects to that Walkman.
Nowadays, ther will be an increased likelihood that the bus or boat that you charter or use as part of the tour will come with a cassette player as part of the sound system. If you are lucky, you may even have a line-level input for connecting the MiniDisc Walkman to the vehicle's sound system.
When you load or unload the passengers, it may be a good idea to always know where the MD Walkman is at all times because these units can be easily stolen by passers-by. You could easily disconnect the unit and take it with you if you are going away from the sound system; so as to dissuade theft.