It is not impossible a feat to pull off, should the opportunity present itself and the individual is expected to step up to the challenge. The most ideal spontaneous presentation would most likely be based on topics that are relatively current and interesting. Therefore keeping abreast with the current events national and internationally will help the individual deliver a content rich presentation which would effectively portray the evident talents. 

People who take the trouble to stay well informed and well connected are usually popularly sought after speakers and presenters as they are usually able to garner the attention of those around easily and comfortably.