Behind almost every good wedding and reception is an equally good backup plan.

Ask any professional event planner. They typically know how to combat the most obvious possible interferences: weather forecasts, shoe-induced blisters or uncomfortable sweat, among other issues.

But even with the strictest itineraries and obsessive, detailed planning, unexpected problems can still arise. Here are a few of these situations, along with possible solutions. (The key is to not panic! Most of these solutions are obvious and easy. And now you’ve run through a plan that you ideally will never have to implement.)

Scenario A half-hour before the wedding, the officiant is nowhere to be found, and there’s no time to book somebody else.

Solution Find someone among your guests who might be properly trained and ordained, said Anthony Navarro, the creative director and owner of Liven It Up Events in Chicago.

But what if no one has the legal credentials? “Whether a family member, or wedding party person, someone would have to perform the ceremony, just for the sake of performing the ceremony,” said Mr. Navarro, who has dealt with this situation twice (in 2012 and 2014) in Chicago.

The legal ceremony would have to happen on a different day, he said. “You’d have to go to a justice of the peace.”

Scenario A zipper splits or a button pops on the garment of a bride, groom or member of the wedding party.

Solution Sew the person into their clothing. (If the wedding is being held at a hotel, this could be easily done by an in-house seamstress.)

“Sewing is an almost-standard wedding thing for us,” said Alyse Erickson, the lead event planner at Every Little Detail in Bloomfield Hills and Lansing, Mich. “We’ve had bridesmaid dresses that didn’t fit, split, and had to sew those back together.”

She also recalled a rather buff groomsmen who didn’t bother to try on his tuxedo before the wedding day. “The buttons wouldn’t stay buttoned,” Ms. Erikson said. She sewed his shirt together as tightly as she could from the inside, “and then buttoned the buttons so it at least looked buttoned.”

Scenario A child scheduled to walk down the aisle as a flower girl or ring bearer refuses. Screaming, crying and hysteria may ensue.

Solution “If they don’t want to go, but they’re not having a freak out, have one of their parents pick them up and walk them down the aisle,” said Mr. Navarro, who has worked with more than 300 children over the last 12 years. “It’s still cute.”

And if they’re having a meltdown, say, at the back of the aisle, “swoop them out of the way,” he said. “A ceremony can be very emotional for family and really close friends of the couple, so when that happens, everybody starts laughing, and it breaks that seriousness before the bride comes down the aisle.”

Scenario A bridesmaid or groomsman gives an inappropriate speech about the bride or groom, with microphone in hand.

Solution Mute the mic.

“We actually went to the D.J. and said we need to cut this short,” Ms. Erickson said. In November 2017, she said, the maid of honor at a 200-person wedding in Grand Ledge, Mich., went rogue, so the D.J. “lowered the sound on her mic, and then people had a hard time hearing her. We all started clapping as if the speech was done. Then, he started playing low music.”

Ms. Erickson, whose business is based in Bloomfield Hills and Lansing, Mich., admits it may sound rude to cut someone off. “You’ve gotta just do it,” she said.

Scenario The D.J. is a no-show. There is no music, speakers, or microphones for toasts.

Solution Immediately contact other wedding D.J.’s in the area. If none are available, phone your local radio station.

“Call anybody you know that would have actual D.J. gear — definitely someone who would have a sound system like that,” said Melissa Hagen, the owner of Melissa Fancy, a destination wedding and event planning business based in Park City, Utah.

In June 2012, Ms. Hagan frantically searched for a D.J. — or at the very least, a microphone — for a Park City wedding. “The microphone piece of it is actually really important for toasts,” she said. “If you can get something like that to solve the problem, that would be fantastic.”

A former radio D.J. filled in, but had he not, Ms. Hagen was already on her way to Best Buy to purchase equipment.

Scenario The bus or limos don’t show up, leaving the bride, groom, wedding party or guests stranded.

Solution Call for a ride — well, several rides.

“We had to order Lyft or Uber, and we had to send everybody in cars,” said Mr. Navarro, whose clients in September 2017 had a 65-person motor coach break down en route to pick up attendees for their Chicago wedding.

“Obviously, it was not cost effective, but in the moment, that’s all you can do,” he said. “If you wait for the bus, you end up pushing everything else back. It ruins the rest of the night.”

Scenario Rain, or snow, is suddenly coming down hard during an outdoor wedding. It’s not letting up anytime soon.

Rain Solution Move the wedding inside. Otherwise, “umbrellas for your guests, and towels to dry seats, are imperative,” said Ms. Erickson, who has worked through seven weddings in summer rainstorms. If the bride gets wet? “Have the dress hanging, and blow dry the dress at a nice distance, so it doesn’t melt any details,” she said. “A lot of times, brides will have hair and makeup artists stay through the ceremony, so there would be somebody there to touch them up.”

Snow Solution Go indoors or cut short the ceremony. At a 125-person garden ceremony in Deer Valley, Utah, everyone, including the photographer, was wiping down wet seats, Ms. Hagen said. “We had to go from a 25-minute ceremony, down to a five-minute ceremony,” she said of the wedding white-out in September 2017. The cocktail hour was also relocated inside. Before walking down the aisle, the groom wrapped himself in a fur blanket from Restoration Hardware.

Scenario The bride or groom becomes ill.

Solution Seek medical attention first.

Ms. Hagen recalls a situation in September 2013 where a bride in Park City actually had dengue fever and was forced to go to the emergency room. “If she hadn’t gone, things could have gone dramatically downhill,” she said.

Ms. Hagen said she spoke with the wedding vendors in preparation for a possible cancellation. “We just had some quick backup plans in place,” she said, noting that any decision would ultimately be up to the bride. She said the bride received “as much hydration and medication as she could and was able to have the ceremony.” She then rested during the cocktail hour, and “after her first dance, she went home.”

Scenario In a Category 3 Hurricane, State of Emergency, the wedding site will not host the event. Airline flights for family and friends are also canceled.

Solution Reschedule for a later date, after the storm.

Hurricane Irene caused drama for an August 2011 wedding in New Jersey. “A tree fell in front of my car on the driveway,” said Kristin Barse, the owner of Bel Momento Weddings & Special Events, which caters to couples in Philadelphia and New Jersey.

Ms. Barse said that her client decided to move the ceremony and reception from its original Jersey Shore location to Central New Jersey, because the bride’s family was so adamant. “Their D.J. was able to come, but he left early,” she said. “He wanted to be off the roads. They shouldn’t have hosted the wedding during the hurricane.”