I think you can see from the replies no one rule holds true for everyone. Whatever works for you can only be found out through a process of trial and error.
Having said that, here's a run down of how I work through my week of commuting. Please excuse the metric thing.
I do a one-way commute of about 19kms - it starts with a 3 km descent followed by a 3 km climb of about 5% average.
I have been commuting now for about two and a half years and have just clocked up 20,000 kms.
The temperature at this time of the year when we start riding is about 5 - 10 C.
In terms of food I have a small bowl of cereal at least one hour before I leave and the mandatory coffee of course. I have a muffin when I get to work.
I take a litre bottle of water for the commute which suffices no matter how hard the ride is.
As far is stretching is concerned, I personally now do a small range of stretches every morning when I get changed at work - part of the getting ready routine - and try and do three nights a week of more intensive stretching when I get home. The reason is I found I was losing flexibility in my hamstrings as my legs bulked up. The other important factor is starting and finishing the week off with easy rides to allow the body to recover properly.