I’ve developed (by no conscious effort or intention) a 3-way system for carrying everyday stuff while riding my bicycle. My system involves my daypack, my messenger pannier, and my man-bag (i.e. a messenger bag that looks a little too much like a big purse).
For the longest time my daypack was good enough. It’s old now — pushing 8 years — and developing various maladies. But I like it because it is light rip-stop nylon. You can stuff the thing silly. It’s accompanied me across North America and to Europe. I’ll use it until it reaches gross structural failure.
So why consider other systems? Well, the big reason is that during hot weather a daypack tends to create a sweaty spot in the center of my back, which defeats my heroic attempts not to sweat at all while riding (imperfectly accomplished to be sure).
The Arkel messenger pannier was an excellent choice to pick up the slack during the hotter times of the year. And that is exactly how I’ve used it — mostly for work or other gotta-dress-nice situations from about early June through September. I don’t use it all year because I don’t really like how it bounces around on my hip while carrying it off the bicycle. It doesn’t drive me nuts or anything. It’s just not as smoothly comfortable as my daypack.
Last winter I was trapped at an outlet mall while certain of my female relatives shopped. I wandered into a leather shop and discovered a nice messenger bag on sale. What the hell. I bought it. I threw it into the mix over the summer as something to carry while riding my Brompton — a little cycle chic flair for the ol’ professor dude. But I began using it more and more because it is comfortable to carry and carries a lot of stuff. It made a good casual choice. I largely abandoned it once cooler weather hit.
So the point of all this is to point out that weather more than convenience has been the deciding factor in choosing what thing to carry to carry stuff in.