Hi, looks like Walgreen's is open on Christmas. Go about one mile west of Old Lake Wilson on Hwy 192 and Walgreens will be on your right across from Formosa Gardens' Blvd and the big shopping center there. They will have reasonably priced staples. You can head there before you check into WH or just a short trip over after settled in.
There are lots of restaurants on the 192 strip including Denny's, Perkin's, and other chains. I am sure you will find something open. It will be a very busy time. In the Formosa Garden's mall just across from Walgreen's are a number of eating places from Giordono's Pizza, Outback, to small take out Chinese and Subway...Not sure if any of those will be open but worth a try.
Another option to check out would be Golden Corral between Old Lake Wilson and Formosa Garden's Blvd. It is a great buffet that is always fresh and good because it is so popular. They offer Christmas hours that "vary by location."
Good Luck...have a great time!!!
Ted