The ingredients are pretty basic too, but there's 11 of them, and you may not have all 11 in your fridge or pantry at this very moment. Still, if you're planning a party, or just making a very large salad, it's well worth making your own ranch dressing from scratch.
Like all the mayonnaise-based dressings, ranch can be made with store-bought mayonnaise. If you want to feel like you did something besides stir, you could always try making your own mayonnaise. But if not, the dressing will still be creamy and tangy and thoroughly excellent. Here's the ranch dressing recipe.