FOOD:I have found it very difficult to find consistent information on the proper diet for a pet duck. Most of the sources I've found agree that a 20% protein, non-medicated chick starter for waterfowl or game birds is appropriate for the first 2-3 weeks and then switching to 14%-16% is better.
I found it nearly impossible to find diets specifically for waterfowl, but I found an unmedicated "Chick Starter/Grower" that was labeled for chickens, ducks, geese, turkeys, and quail that had 20% protein at a local Tractor Supply store. It is made by the Purina company for Tractor Supply under the brand name "DuMor" and cost $6.59 for a 20lb bag. It says on the label that it can be used for ducklings up to 10 weeks old, but it is my understanding that this is aimed at birds intended for meat. Such a high level of protein can cause medical problems if fed too long, and should be avoided in pet birds.
They have another formula called "Poultry Grower/Finisher" that is 15% protein and is labeled for use in poultry and waterfowl. That is the diet I plan to start switching them to at 3 weeks of age. When they reach 10 weeks of age, I'll start supplementing their feed with scratch grains, and of course by that time they will be old enough to forage in my yard as well. If they do turn out to be girls, I'll give them a laying feed once they start laying eggs.
WATER:I use a small bottle-style automatic chick waterer, which I find they foul very quickly. I change it two to three times a day, depending on whether I'm working or at home. I find that they put things in the water on purpose so they can chase them. It seems to be their favorite game! It doesn't do any good to change it more often than I do because they literally foul it up within ten minutes. It does help prevent bacteria from catching hold to change it at least morning and night. I use straight tap water for them. I was afraid filtered water would be more prone to bacterial growth.
BEDDING:I use wood shavings I bought at the Tractor Supply. Its super cheap and absorbent, and the chicks seem to enjoy playing with it in their water dish.
MISCELLANEOUS: I feed them using one of those aluminum chick feeders with the little holes all around that you can screw a mason jar onto. I don't use the jar since I have only two ducks and I change out their food each morning. I find it works better than the open dish I used the first day because they have a much harder time pooping in it, and two days in a row now they have been completely unsuccessful!
Ducks need grit. I use the granite chick grit from the tractor supply for them. I offer it in a tiny ceramic hamster bowl I got at Petsmart next to their food dish. You can mix it into their feed, but I prefer to offer it separately and they take it as they need it with no problem.
I also got them some Benebac bird paste from work. It is a pro-biotic for birds and reptiles which is helpful for intestinal health. It is recommended during food changes and stressful situations.