Some sites have a ton of product, and some don’t. This is much more applicable to sites that have lots of product.
When a shopper is trying to find something, they are going to search for it. Step 1- make sure the search bar is large and well placed. But then, how will they know if what they are finding is actually what they’re searching for?
Sears takes autocomplete to the next level by showing you top search results within the autocomplete box itself. Its surprising at first, but then quickly becomes intuitive and awesome.