At this time- whatever you have worn into the park is fine. There is a rumor that it is changing to a signature, so if that happens, they tend to like guests a little dressier.
For the majority of the restaurants, acceptable park attire is just fine. For the signatures, it isn't much different, just slightly up the dressy scale. (No torn clothing, swimsuits or cover ups, tank tops, inappropriate t-shirts, stuff like that)