Accessories are a must when it comes to being Kate Middleton for Halloween.
The most important accessory: the engagement ring. As long as you have long brown hair (or a long brown wig) and are wearing a replica of that ring for Halloween, most people will know who you are no matter what clothes you're wearing.
If you're going for the wedding day look of Kate Middleton, than a tiara is a must.
(they have replicas of what she wore available, but I picked out an inexpensive substitute)
This should also be paired with a bridal veil. (I'll be using the veil I wore at my bachelorette party)
Check out the start of how I made my halloween costume as the Duchess of Cambridge
here. Or, click on the label "William and Kate" on the side of my blog.
If you're going as "Princess Kate" for Halloween too, don't forget your bridal bouquet!