1. Make it legal: Somewhere in the last 30 or so days before you get married, you'll need to go down to the town hall or county clerk's office where your ceremony will take place and apply for your marriage license. Depending on the state, there may be a waiting period between when you receive the license and when you can get married, so don't wait until the day before.
2. Meet with vendors to fine tune the details: If you're doing it on your own, schedule meetings -- or perhaps a Skype or Facetime appointment if you're planning from afar -- with your vendors to go over all the details to ensure that you haven't missed anything. Before you speak to them, run through everything with your mom, fiance, or someone you know who's either married or has a lot of experience with weddings to get their take.
If you've enlisted a planner, your planner should hold a final meeting with you to go over all the details and make sure you're happy with everything you've selected. We show our bridal couples a mock up of their tables with the exact linens selected and a sample of their centerpiece so they can see exactly what they'll be getting on their wedding day.
As you're talking to the vendors, put together a timeline for your wedding, including any events happening before and after the ceremony and reception (the rehearsal, a brunch etc). Your planner and their team will manage that for you, but if you don't have a planner, put someone you trust in charge of keeping an eye on timing and logistics.
While you have them on the phone or in person, confirm with the vendors the balance remaining and how they want the bill paid. You can prepare envelopes with checks and any tips ahead of time.
4. Organize accessories, decor, and honeymoon items you'll need to transport: The author of this article has a great idea - she suggests having separate baskets for fashion accessories, ceremony decor, reception decor, and honeymoon items. In your fashion basket, keep your jewelry, shoes, and somethings old, new, borrowed, and blue (if you're following that tradition) together. The ceremony basket may contain a glass to break, CD or iPod with music you want played, unity candles, or the programs. Your reception basket may have a more comfortable pair of shoes, your cake topper, and anything else you'll be bringing to the venue ahead of time. Think about what you might encounter on your wedding day and plan ahead: sunglasses for a sunny day or a wrap in case it will be cool.
If you have a wedding planner, consider having them put together an emergency kit/amenities basket for the bathroom so you and your party (and guests) have access to the essentials you might need: spray deodorant, mints, headache medicine, scissors, needle and thread, and so on. If you don't have a planner, you could enlist a family member or bridesmaid to help you pull this together on your own.
Unless your honeymoon is a surprise (romantic!), you can probably pack ahead of time for your honeymoon. You definitely don't want to be doing this the night before your wedding or right after it, either. Have someone you trust handle transporting your gifts and cards to your house or a safe place where you can retrieve them when you return.
I can tell you from personal experience that this is good advice: I held my makeup trial only one week before my wedding and, though it had never happened before or since, whatever foundation or undereye cream my makeup artist used made my eyes puff up like crazy. Luckily it went down about three days before the wedding, but I was panicking. I also had to make sure my makeup artist could find an alternative that hopefully wouldn't cause the same reaction (she did, and it didn't).
One of our extremely experienced planners also suggests scheduling your hair and makeup appointments on the day of a special event, like your shower or bachelorette party, or most usefully, on the day of one of your dress fittings. Have your hair and makeup done first, go to the salon, and try on your dress: you'll see exactly how you will look and if you end up not liking the style as much as you thought you would, you still have time to make adjustments.
If you're paying for any of your bridal party to get treatments, manicures, or hair and makeup (or if they will be paying for themselves), be sure to schedule that and build in enough time for everyone to get done.
The article also touches on additional details like figuring out the seating chart and preparing for out-of-town guests. No matter how much or little is left on your to do list, perhaps the last thing on this list is actually the most important: Repeat after us: Everything will turn out great.