For myself, I recently ran a one-shot for Free RPG day at my FLCBS. After spending a couple weeks panicking and trying to find the perfect scenario online, I ended up creating something from scratch. Here's the blurb my lovely editor wife helped me write up for them to post to their announcement:
Hurricane Phillip is bearing down on the Gulf Coast and the people of Illedesante, LA are gathering at their makeshift emergency shelter: the high ground of the local gymnasium. However, the inclement weather is only one of the terrifying trials the players must survive this night; an ancient cult lurks within the swamps with sinister designs on the town and those held captive by the storm.
I had enough pre-gens for 6 people. My wife and her nephew were the only two I was sure would be there, but a friend showed up from our regular gaming group, bringing the total to 3. A coworker texted that he was on his way if there were any seats left, so I said "yes."
Then it was announced that one of the tables scheduled that day had an illness and was canceled, so immediately, 5 people walked up looking to play. I was gobsmacked, as now there were 8+1 on the way. I quickly texted back "full table" to my coworker, while my wife and our friend offered to bow out. I pulled out my spare char sheet that I like to keep for reference and passed it to our gamer friend along with another pregen and said "copy this." Meanwhile my wife offered to ride-along with her nephew.
Now with 7 players (dear lord I hate more than 4, and we were at 6+) I was taking at least half the table of newbies through what was about to be a playtest of my campaign. That said, the table was phenomenal. The players were eager & engaged! Somehow, I was able to keep the large (split) party all on track and everyone was laughing and having a good time. I can't remember the last great Keeping experience I've had like that, but it's been far too long.
For anyone interested, here's the spoilers on the rest of the campaign.
spoiler
The gymnasium is full of townsfolk who could ride the storm out well enough, assuming that the insular deep-one hybrid family (the Dufrense) underneath the nearby levy were not planning to blow it up. The hurricane was causing the salt-water to flow inland, enough that a submerged entity could survive (it cannot survive in fresh water). Once the salinity was high enough behind the levy, the family would enact a ritual to awaken the monster and blow the levy, letting it wash through town (snack on the townspeople) and drift out to sea.
The investigators had to put together a handful of clues. First that the Dufrense had stolen dynamite from a local construction site. My players immediately came up with an Al Queda/9-11 angle based on timing and locale, which was wonderful color for the scenario. The Dufrense then kidnapped part of a family seeking refuge, planning to use them as sacrifice in their ritual. Now that the players had identified the family as the problem, I set up for them to inquire with the townsfolk about the family as to their motivations. They learned that the family was "weird looking" (Innsmouth look). Only the younger family members ever came into town. An elderly person remembered that they probably kidnapped one of her classmates years before. The town drunk had accidentally wandered onto their land and saw that they had a "Church that weren't no Christian church" on their property. And lastly, an engineer sent to keep an eye on the levies talked about how intensely interested the family was in the "weak points."
Armed with this knowledge, the investigators split into two groups "assault the church" and "assault the levy." Through a lot of botched (and a few very successful) rolls, they managed to destroy the one artifact that could somewhat control the entity, but also managed to stop the ritual before it completed. They also managed to stop the two cultists who were going to blow the levy, and recover the dynamite. Because this was a one-shot (and I allowed that they were near the end of the scenario) two players opted to carry the recovered dynamite into the well where the entity was sleeping, and take out the entity in an explosion.