I am going to address only the stretching portion of the question since some misinformation is out there. When you say stretching, I hope you mean dynamic as opposed to static stretching especially if you are about to compete in a sport. If you are referring to static stretching, taking a shower may be a better option then, but if you mean dynamic stretching, a shower will not provide a greater benefit.
For peak performance, athletes or weekend warriors should use dynamic stretching prior to an event.
In previous research it has been recommended to use dynamic stretching as the primary method of stretching pre-event warm-up before high speed, and power activities (Little & Williams, 2004). The findings of this study agree with that recommendation for agility activities as well. This study supported the use of dynamic stretching in eliciting the greatest performance in agility movements by decreased T-Drill time. The findings
of the current study are consistent with those of Fletcher and Jones (2004), and Young and Behm (2003) who determined that dynamic stretching elicits the best performance in power and high-speed activities .
However, static stretching does not improve performance and can actually lead to injury.
The current study found static stretching to have a negative effect on agility, and acceleration (Fletcher & Jones, 2004; Nelson et al., 2005). As acceleration is a component of agility, these findings support those of Fletcher and Jones (2004) and Nelson et al. (2005). Agility also involves components of braking, and change of direction. Static stretching prior to agility activities was found to have a negative effect on agility performance .
To read up on dynamic and static stretching as well as other types of stretching, I would recommend MIT's Types of Stretching page.
Additionally, the references to my reference one provides many more useful articles to look into.
- Static versus dynamic stretching effect on agility and performance