I see people always asking "what can I give my ducks as a treat?". Well there are many options.
My most used one are:
Anything like pumpkin or cantaloupe that have huge seeds in, you want to remove them. Those seeds can cause an impacted crop or giving ducks too many smaller seeds can also cause an impacted crop. Any thing like apples, pears, and cherries should always have their seeds removed. I personally play it safe and never give my ducks seeds. Pumpkin seeds is ground up and given to ducks can be used as a natural worming.
I tend to mix different treats in a large bowl with cooked rice so that I can give every duck a nice treat with-out going broke. I just buy the instant rice at any grocery store. Rice is also something I keep warm in the winter to give as a warm treat to the ducks. For the summer you can take any of their treats you would give and dice them up, put them in water, and then freeze it. You can place these cubes of surprise treats in their pools or just on the ground and they can have fun trying to dig out the tasty treats!
Ducks also love meat! Who would have thought?? If I get a rotisserie chicken and do not finish it I will pull it apart and give it to my ducks along with cooked hot dogs. Ducks are omnivores and it's okay to feed them meat.
Another thing you can give them is the eggs you do not want. That is an excellent way to give them calcium. I will give my ducks even the shells from breakfast. When they see me walking with shells all the ducks get very loud and come running! They sometimes fight over the shells and chase each other which is fun to watch.
For more about Treats for Ducks check out this Amazing reference from Backyardchickens.
I am always going back and checking that to make sure I am not going to be giving them anything they are not supposed to have.