I did a cruise from Budapest to Strasbourg in 2016. I was told by a JY telephone agent that unless I took the full excursion package I might not be able to book on board, and if I could, I might not be on an English speaking tour. This was not the case on my cruise. Half of the group had pre booked the package, others booked the tours they wanted on board, or, in some cases, went off the ship, by themselves. I’m not sure which cruise you are thinking of, but do bear in mind that river cruises don’t always moor within easy walking distance of cities, and on occasion, the ship, will move on after excursion passangers have disembarked, and they will rejoin at another location. I suggest that you ask JY for full details of the excursions offered before making your decision.