This is a great question. I've had many great modules with only 2 days notice, and here's a few ways that I deal with tight deadlines for modules...
Make a Triage
Choose a Primary, Secondary and Tertiary idea that you would like to have in your module. These can be anything you would like, such as monsters you think are cool, genres you like or a particular game mechanic you'd like to focus on. An example would be an espionage story with a Human Assassin who tries to run from the players through a crowded city square (skill challenge). Take your primary idea and make a hook that will goad the players towards this event/mechanic/goal/doom!
Pick some Padding Elements
I hate to compare this to how you would write a college term paper, but... well... you know :) Players can spend a lot of time in a city asking questions if they have something interesting to investigate. If they have a far destination, nervous nights guarding the camp fire with a few light encounters can add some engrossing realism. Always have a few generic monsters written down for random encounters. When in doubt, throw a few of these guys at the party. Be ready with a few NPCs for the party to interact with. The key here is to add fluff with something rewarding. EXP, gold, treasures or details to help the mission.
Get Good at Improv
"Laying track while the train is rolling" is the best way to describe this. This is a skill learned with time, but if you can focus on a few details that are important, and the tools you have available, you can make a module out of a few bullet points easily. It will help to focus on your Triage and just make a snap decision that makes sense in the moment. There are lots of great sources for Improv, but one of my favorites is the "yes, and" exercise. If a player wants to do something, say yes! This has lead to long sequences that required no preparation on my part that the players loved. Just play within the rules, and revel in the surprise with them. This is pretty much free gameplay since you are letting them dictate the direction. Just remember your three ideas, and poke the game in that direction slightly every now and then.
In closing, this is an opportunity to let a game grow from very little and could reveal some fantastic spontaneous gameplay. The best part of this is you will likely get more honest ideas of your players personalities and how they think, which feeds you new content for later modules.