Over time I figured that the right hand pannier was best for clothes and the left for clean up gear. Why?? I don't know.. It worked out that way, but I think in part it's because I park my bike on the left side of my desk which put the clothes and shoes close to hand, but your results may vary and you may want to experiment to see what works best for you
Like anything else, the best way to pack for cyclecommuting is to plan ahead. I typically leave the bike pre-packed with as much gear as I'm able which saves at least a half hour of prep time on the morning of departure.
I pack my panniers so that everthing is modular and can be removed and re-inserted easily. My clothes are folded so that they are as narrow as possible and then rolled up.
The first step is to fold my slacks in half at the knee as if I were hanging them on a hanger:
The next step is to flip it over so the now folded legs face upward:
Next fold them longitudally so that it resembels a length of 2 by 4:
Next move on to folding the shirt. I usually start out folding it similar to how it came out of it's original package like so:
Then fold this package longitudinally:
Then present the shirt on top of the folded pants. It's best to match the widest part of the shirt (Usually the collar end) with the widest part of the pants (the folded waistband).
The next step is to roll up the shirt and pants like a sleeping bag starting from the widest end and ending with the narrowest:
Then using the belt (I have more than one of the same type so I don't need to break things apart when I need this particular style of belt for other functions.) cinch up the bundle.
Typically I would then put the bundle in a plastic grocery bag. Why? For starters, the bundle bulges out of the pannier a bit and once prior to taking this step I was caught in a thunderstorm that thoroughly saturated this pack of outerwear. Secondly, it helps keep the extra loose end of the belt from flopping out of the pannier and getting caught in the spokes or dragging.
Here is a pictoral overview of everything that is pre-packed the night before in my right hand panniers:
Left shoe, T-shirt, Underwear, sock bundle, cargo web bungee, Outerwear bundle, right shoe.
The T-shirt is folded like the outerwear shirt and rolled up. It's then stuffed in the left shoe. The sock and the underwear are stuffed in the right shoe.
(Not Shown) I pack the pannier-hood pocket just prior to departure and in it I keep my glasses in a rigd case as well as alternate sunglass lenses in my sunglass case and the spare cargo web bungee .
The first step is to insert the shoes into the pannier. I usually insert them so the soles are facing towards the wheels. It's mainly to keep any loose clothes clean that I might shove into it in the future.
The outerwear roll is then pushed down over the shoes.
Here is the now loaded pannier mounted on the bike:
The rolled up T-shirt in the pannier bungee is used as a rag for cleaning rain smudged eye glasses
The left pannier carries toiletries and a towel for showering. The towel is folded in thirds so that it is narrow enough to fit in the pannier. The shaving kit is placed in the pannier-hood pocket along with my electric razor. I found a typical shaving kit to be a little large for the pannier-hood pocket; however, a case for a blood pressure cuff turns out to be just the right size. I imagine that there are shaving kit bags of similar size available and that's what I'd recommend.
One of the last things that gets packed and is usually laid right on top of the towel is the charger for my niterider Digital Evolution headlight. During spring and summer I only need the headlight in the morning; however, to cover contingencies I tend to charge the battery that I used to get to work immediately upon arrival. The reason being that if on the way home I make a stop either scheduled or unscheduled (like for a beer at Kennally's Irish pub) the light is ready for use if I don't leave until after the sun goes down.
The shaving kit contains a bar of soap in a traveling soap dish, toothbrush, toothpaste, a comb, a small hotel size bottle of shampoo, and a can of deodorant. I suppose if you're into it you could include a small bottle of foo foo/Colóne/ aftershave, but I've never been into that sort of thing.