As mentioned in SA forum, there is a Rudy's BBQ as well in New B. Jonny Carino's is next door and a Mexcian restaurant as well.
Schlitterbahn is a blast, you will have a great time. I would suggest The Gristmill for dinner, it is a really fun place with great food. It is in Gruene, which is only about 5 miles from downtown New Braunfels. Anyone that works at Schlitterbahn will be able to tell you how to get there.
Gruene is a really neat little historic town, with shops and an awesome (and slightly famous as far as Texas music goes) little bar, Gruene Hall. So if there is a wait, you can mill around. The Gristmill is HUGE, pretty casual, and hangs right above the river (so sit outside if you can). We always get the chicken fried steak, but it has burgers and steaks, etc. I've eaten there about a dozen times and I always have a great time and meal. Here is the website, FYI
I second the Gristmill - the food was wonderful and the atmosphere was really nice. Ask for a spot near the creek where the walls are open.
There is a local restaurant on the same main drag as the waterpark, I think it was called Pat's Place Restaurant. It was really good and the place was packed.
Union St. Station was wonderful for breakfast
The water park is a blast! Have fun
What are the prices like at the Gristmill? We'll have four kids with us. Thanks!
Here's the link http://gristmillrestaurant.com/menu.html
I would suggest Clear Springs Cafe. Every time i visit New Braunfels i have to eat here. They have the best onion rings you will ever eat. I know Rudy's BBQ is very popular but I do not recommend it. Also a stop in Gruene is a must when going to New Braunfels.
Pats Place is a local favorite and its right there near Schilltterbahn, you could walk there when you are done at the water park, they have the best ice tea, my son loves the philly cheese steak but they also have fried shrimp, Chicken fried steak etc..I love their fired pickles.They have been here since the 70's I think...
Also Gruene River Grill is great if you are going to go to Gruene, great steaks!! by the way Gruene is in New Braunfels its just like a very old part but very neat.
Absolutely go to the Gristmill if you can! Also, New Braunfels Smokehouse is really good, especially for breakfast.
Second on Pats Place. Good food and local too. Only a block or two from Schlitterbahn also. I always try to eat at local joints when I can. It is just usually better.