Oost is the easy side for eating afloat. This is a pick-list, not a route: most crews tie up at one, maybe two and make an afternoon of it. Pick what suits the day and the wind.
Three to start with, all on the Amstel side. Ode aan de Amstel and Amstelhaven sit right on the Amstel with their own dock, and Amstelhaven will even bring the order down to the boat. A little east, there is a beer under the De Gooyer windmill at Brouwerij 't IJ.
A few honest notes. The terraces fill fast on a warm afternoon, so an early table beats a late one. Some are proper sit-down kitchens and some are quick stops, so check the spot before you plan the meal around it. And the docks are first come, first served, with the signs always the final word, so read them before you settle in.