I like to be over prepared most of the time in most aspects of my life. It keeps me organized, sane, and calm to know that I am prepared for almost anything life might throw my way. That is just my every day life.
Imagine how I amp this up as a wedding planner on the day of a wedding. You can bet, I have the biggest bridal emergency kit you have ever seen. It is in a steel case (cause you never know about the weather) with compartments that expand after you open it. (If you carry this much stuff, best to be able to see most of it at a glance.)
Funny story: I once had a groom ask me for things from my emergency kit (comb, eye glass wipe, shoe polish) and I gave it to him thinking he actually needed these things. It wasn't until he asked for really random stuff (harmonica, shoulder pads, wig piece) that I knew he wanted to see if I had a Mary Poppins bag. He finally asked me for a hammer. I told him I didn't have in my kit. It was in my purse. He looked at me a little scared. As he should.
Here is an excellent infographic on the items you might want to include in your bridal emergency kit.