When you are booking your trip ask your TA to see if you can purchase extra baggage weight at a reduced cost. We flew with Sunwing and were able to arrange an additional 30kg ahead of time for about $150 (plus we got upgraded seats). Or if you're not using a TA, call the airline and see if you can arrange something. They usually are very accomadating to brides, especially if they know ahead of time that you will have extra luggage (that way they can plan ahead, ie. not take as much cargo).
Also when thinking about what to bring down, plan! We brought down paper lanterns, which fold flat. So they don't take much room. Most OOT bag items were small, or flat- so packing them was not difficult. When we arrived in Mexico (we got there 2 days in advance of our guests), we went out and bought stuff locally, such as treats, snacks, and the vases we used for our center pieces. This way we didn't have to travel with it, and it was cheap down there anyway! Plus our guests LOVED the local treats- it gave the OOT bags a Mexican flare.
Also be ready to have your baggage inspected at the airport. If you get the 'red' light, or if you have a lot of extra baggage they will likely want to look. We tried to keep all our decor and OOT bag stuff together so that it was organized, and we had the reciepts in hand. Explain that you are getting married in Mexico and it is gifts for your guests. (they are worried sometimes that this stuff might be brought into Mexico to be sold. Which they prohibit)