Ask your parents and check at bridal shops and vintage clothing stores. Food and beverages can be as easy as chips, soda, veggies, etc or an elaborate meal. Again, it's all about budget. Use lots of cowboy hats, maybe even as favors and that red western bandana theme. See if you can get some borrowed saddles and put them on saw horses and pumpkins and hay around.
Corn stalks are also good.
Surround with narrow rope to look like lassos and have balloons with western design tied to them. I am a parent on the graduation tea committee for the class of 1999. We first need to decide what the theme will be for the event. If you have any suggestions or ideas for a theme please e-mail me. Thanks for your time.