Schoepf's BBQ on Central Avenue in Belton offers pit smoked brisket, steak, pork chops, chicken, sausage etc. with a choice of sides. It's rustic with wooden picnic tables. You choose your meat from the pit and your sides from the counter inside.
Luigi's Italian Restaurant in Belton is not too far from the pavilion at the lake where the bash will take place. It is across from the high school on Loop 121 where it meets Lake Road. Lake Road is the one that the dam road intersects at the pavilion at Lake Belton. Because they are so near the school, they have no alcohol license but the food is good.
BJ's Restaurant in Temple at the intersection of IH35 and the HK Dodgen Loop - in the shopping center - is a sort of modern grill and drinks house. It's a bit noisy - by design I think - but is fun occasionally. They keep a fairly well stocked bar.
There is a semi-upscale steak house in downtown Temple called Cheeves Brothers. I say semi because the prices are high and the service is generally good but I think the steaks are average. They do have a decent dessert cart, IIRC. It is located at the corner of Second St. and East Ave. A. Reservations might be needed on a Friday night.
There is a Longhorn's Steak House (chain outlet) on the northbound frontage road between Midway Drive and the aforementioned HK Dodgen Loop.
There is a sushi restaurant downtown called Nami. They have another place in Belton. The one downtown is on Second Street at East Ave. A across Second Street from Cheeves Brothers (I think).
There is an Italian restaurant downtown called Pignetti's. It is on Second Street in the block above East Ave. A. I find it noisy and the food from average to good. They have a good wine selection.
There is a restaurant in downtown Temple called Benny's Ristorante. It was formerly an Italian restaurant called Dibz in a different location. I've heard that the menu has changed and expanded but I have not been there and cannot attest to its quality. It is located on S. Main St. near East Ave. A.
There is a Thai restaurant on West Adams Avenue called Mi Mi's. Good service and pretty good Thai food. Mi Mi is a native of Thailand and serves authentic food from fresh ingredients she chooses each day. They have a good assortment of Asian beers.
I hope this helps. I believe you can find web sites for all these places but I'm not sure of that.
Those are the ones I can remember off hand. Maybe Paul will chime in with his favs.