No Prep, No Problem
Contrary to popular belief, GMs do not always need to have an intricate plan in advance. One day when I found myself in charge without any warning, I realized I would have to {cue dramatic music} “wing it.”
Blasphemy, you say! A GM cannot be a real GM without prepared material! The adventure would fall to pieces! Until that fateful night, I would have totally agreed with you. Yet amazingly, this game went well. The D&D Police did not show up. Most relieving of all, my players did not even seem to notice.
The first thing I did was a dramatic summary of the campaign up to tonight. Notes are invaluable but the GM has enough on their plate so have someone else take them each session. I then told the players they had several minutes to discuss their plans amongst themselves. This gave me additional time to get myself situated behind the screen. This allowed me to setup a new plot hook that I created out of old campaign elements. Campaign elements that were essentially given to me during the summary as well as listening to the players discuss their options. Basically idea recycling can help compensate for lack of a formal prep.
Next I let the characters automatically run into a random encounter. This was easy to implement, a fun combat for the players, and ate up some time. Presented the right way many random encounters can appear to be ‘normal’ encounters. In fact, next time you are reading a module, be sure to check out those tables or any other optional side quests the writers took time to come up with as you can find worthwhile material in them.
Afterward, I was ready to move the plot forward. The party had just retrieved an item from the city’s sewers for an NPC (overthrown goblin king) who informed them that they needed to go back to that same area to get an additional item that was “necessary.” The players weren’t happy about this, but the stubborn NPC (supported with the fact that he ‘happened’ to have enough power to back up his orders) made them retrace the path from the previous session! So the right command by an NPC who can enforce their decrees if necessary serves as the in-game tool for manipulating situations to how you need them to be.
Finally, whenever necessary I threw in a few doses of the classic GM trick: ‘Fake Rolling.’ By this I refer to the age old practice of dropping dice behind the screen and looking down, but already having the outcome planned. No, this is not cheating. This is a discrete way to direct the outcome in the best interests of the game through a believable technique. In the case of an evening you’re not fully prepared for, its an essential tactic to get you through the night.
A few tips for when you yourself discover that Murphy’s Law has decided you must wing it:
1) Have an intermission. At a suitable stopping point, let everyone stretch, get something to drink, talk for a bit, etc. Call everyone back after you’re ready for the next stage.
2) Include home-made monsters for interesting game play and to create surprise. Shift a cliche creature into a “WTF is that?!” with just a few attribute changes. Templates are invaluable for fast fixing. When players fight the unknown, they are a lot more cautious and combats will take longer.
3) Familiar territory can become unfamiliar territory with a simple eclipse or an earthquake. Changes in the terrain or weather will add to delay, either through investigation or setting a new course around.
4) If it fits the situation, break out an actual in-game game such as Three Dragon Ante. Have an NPC request a game, perhaps setting stakes that are too good to resist.
5) Likewise consider an in-depth roleplay over a meal. Check out this recent DMing article, Gaming Goodies, for how to do that on a budget.
Hopefully this advice will be useful to you the next time you have to wing a session. It happens to everyone, and it will eventually happen to you. Just keep cool, announce an intermission, and if need be, have the princess fall down an earthquake-induced chasm after ‘rolling for it’ behind the screen. Yeah, that’ll keep ’em busy for awhile.

I am called Wing for a reason, actually.
See, due to limited time and a rather limited attention span aswell, I usually have little time to prepare things propperly. Not to mention that my players never. EVER. do what I’d expect them to. Therefor, I wing it. Always. Though not entierly. I do what I call “floating DMing”. Namely, I aopt a few rules.
I prepare for nothing specific. That is to say, I plan specific events that WILL happen. By preparing encounters and challanges ahead of time as well as the important story scenes I can allow the characters to run the game as they will and simply adjust and include theese encounters, challanges and scenes accordinly with no absolute planned order.
If I planned for them to go on the river and be ambused by suahaugin and they decide to take another path towards whatever goal has been set, I quickly convert theese suahaugin to, say, kobolds, bandits, wild animals. Whatever fits the new path. Unless I allready had planned encounters for every type of travel. (which I often do) mind you encounters do no need to be fights. Skill challanges or other things the characters must overcome are encounters too.
And I, as per my favorite rule of the PHB 4th, say yes. A player has a good idea? I say yes. Then quickly throw togather how that option would work in the loosely floating parameters I have allready made up and established.
For example, My players were in a crook town and the resident articifier and alchemist suddenly decided to pick up new reagents and other materials. Now, I planned for this li