Have you ever been in a situation where a project happens to drop in your lap and it needs to start like yesterday? If so there are 2 key items you need to get it going.
They are: a Project Charter and a High Level WBS.
Many times for small internal projects (my definition of small is less then 8 stakeholders, 15-20 items on the WBS, no budget and a project duration of 8 or less weeks) I put together a Project Charter, but also include things in it which you would typically find in the Project Plan. Like a list of upfront risks, and the communication plan.
Next I take my High Level WBS (which I created using historical information and having short meetings with the stakeholders) and put it into Visio using their timeline template.
Then it is time for the kick-off meeting where we review the scope, the Visio timeline, update the timeline, discuss the risks and touch upon the communication plan.
The Project Charter and WBS are the 2 key items that every project, big or small, needs to have.