There are some restaurants with a 'dress code' now - Cali Grill is one. The dress code is pretty casual though - they allow t-shirts and shorts. Just no tank tops, bathing suits, ripped clothes or offensive sayings. Oh, and no flip flops - I think that just about covers it.
If we go back to the resort mid-day we change - and usually shower, but not always. In the summer heat, I'd be more inclined to take a break mid-day.
I really like to wear anything with lots of good pockets - so I prefer khaki's over jeans most days. I look for ones with knee pockets that button or zip. Usually they aren't too hard to find. The trouble is finding something that doesn't wrinkle up when you wash it. For guys that's really easy, for women it's much harder. The long shorts that are popular this summer are great.
One of my all-time favorite outfits was my outfit for AK from a few years ago. Often we jet over to AKL and Boma for dinner, so no chance to go back to the room before dinner....but we also like to ride Cali river Rapids sometimes - or at least I do...So I'd wear khaki pants, and under that i had a dark green tankini swimsuit. It was such that the top didn't really look like a swimsuit - more like a nice tank top. Over that - I have a really pretty sweater that had a really open weave. Almost like a mesh, but much nicer looking. It was perfect. Put it over the swimsuit top for dinner and it really didn't look at all like a swim suit - yet if the outfit got wet on Kali it was fine. Since it's a tankini, using the rest room over the day is easy. Sadly, the bathing suit is worn out now.
I also liked board shorts for a while. Even though they don't have pockets to speak of, they dry quickly if they get wet, and are great in the heat. They aren't the style as much now, and you've got to have your weight down to wear them as every bit of fat shows through. But they are/were great park gear.
If it's cooler in the evening, then we switch to long pants. Sometimes jeans - like for MK in February.
Often during the day, if we've got a stroller, then we bring a dark sweater or sweatshirt. A color like gray, dark green, black will not show dirt quickly. (White and EVERYTHING shows, then you're stuck wearing it until you can get back tot he room). I prefer something with a zippered front and a hood. That way the item can double as rain gear, as long as there isn't a downpour. Even when it's pretty warm, some of the interior restaurants can be cool withthe AC and having a cover is great. Conversely, a lightweight cover can help if you feel like you've had too much sun. So it depends on the expected weather which cover-up I choose. A nice black sweater can dress up any tank-style top for dinner.