I currently have six months worth of food and water, and intend to cache more elsewhere. I made it a point to taste all of it before buying more to avoid all the crappy tasting foods. Also a good supply of personal items(toilet paper, soap) is a must. Don't forget to get extra for trading. I also went through some serious survival training. A couple years ago I set a plan in case I have to leave the area. I have several ways out in case Highways or Freeways are blocked. I also have a totally rural dirt road/back road/cow trail escape route just in case. Don't let anyone laugh at you. You're better safe than sorry.
In one recent 10-year period alone, over 200 military incursions were conducted by the Mexican army into the U.S. border states of Arizona, California, and Texas.