According the weather conditions of the past years, Beijing and Shanghai will be very warm in middle April and May. Blouse, T-shirt and skirt will be very helpful.However, sometimes, the weather is unsettled. You'd better carry a windproof coat.On the cruise ship, the weather sometimes is quite windy.

As for more tips of Yangtze Cruise, you can read the following page for reference:

https://www.travelchinaguide.com/cruise/tips/packing.htm