OP, I think you are getting some confusing answers. If you want to buy a one day MYW ticket and add some water park options, you will still only be able to get into a park (MK in your case) on one day. There's no reason to add the park hopper option for a one day ticket - you would spend a lot of money for something you probably wouldn't use, since you plan to spend a full day at MK, right? Adding the park hopper option doesn't let you go into other parks on another day UNLESS you also have bought admission tickets for that day as well.
You'll be able to use up those dining credits at the resort restaurants, though, and that would be fun!!
But no going into a park for a meal without a ticket for that park, sorry.