Having a little bag that you can carry (or have someone in the bridal party carry) with you throughout the wedding day can keep you from worrying about things that may happen, and dealing with them when they do.

Medicine

Although everyone is feeling wonderful on the wedding day, its amazing what a few nerves can do to the body. Headaches, upset stomachs, and dizziness can all rear their ugly heads right when you are feeling the most pressure.

And thats not just the couple.

You may want to keep on hand a few things to keep everyone feeling good, or at least keep them upright throughout the ceremony. A chewable or liquid antacid is a great way to calm any nervous stomachs. Crackers and ginger ale are good though too. For headaches, you can keep some acetaminophen on hand. This is usually gentler on the stomach than ibuprofen, and can be taken without food.

If the bride or bridesmaids should feel dizzy, then have them immediately sit down. Dizziness can be caused by a lot of thingslow blood sugar, nerves, and more serious conditions. If the bride or groom should faint, smelling salts can help to revive them.

Bandaids are good too for sore feet in too tight of shoes.
Beauty fixes

For the women, you may want to have a few beauty tools to keep everyone looking their best. Spare lip gloss and balm are good to keep the lips looking good. A translucent face powder will keep the nose and forehead from shining. Always keep a small bottle of clear nail polish as well. This is good for fixing rhinestones that have fallen off dresses to sealing tears in stockings.

A small brush and mirror can also help, while hair spray and extra deodorant are also nice to have on hand. Bobby pins can help most hair crises, but a curling iron can be an asset too.

Miscellaneous

Its amazing what you may need and never think of. For example, did you think to bring extra straight pins for the corsages or in case the bouquets fell apart? A small sewing kit is good to in order to fix up any small emergencies.

Stain remover and chalk are also good to have on hand. If there should be any stains that need removing, the stain remover is there. If theres something on the brides dress, then you can lightly cover it with the chalkit works great and wont hurt the dress.