Gas prices are back on their way up, making the savings from biking even bigger. So it's time for another episode of Biking as an Effective Means of Transportation, a series that will end someday when I run out of things to say.
Part V covered rain gear, but I haven't talked about what to wear when it's not raining.
First, you absolutely don't have to wear brightly colored skintight lycra. That's for racers or people who (for whatever crazy reason) want to look like racers.
But beyond saying what you shouldn't feel obligated to wear, it's hard to say much, as what you should wear depends so much on your particular circumstances. How long is your ride? What's the weather (and what's it going to be like on your ride home)? Do you need more formal clothes at your destination? Can you and will you need to shower there?
So here are some guidelines: for the ride, dress in easily removable layers. In cold weather, layers keep you warmer; in most weather, you'll want to remove some layers as you warm up. Plan ahead to have a pannier or trunk bag to put the layers you take off. Jackets with zippered vents offer a nice way to control your temperature.
For longer or hotter rides, the sort of high-tech moisture-wicking clothes available at sports or camping stores may be useful (but, again, it doesn't have to look like bike racing gear.) Wear something you're comfortable moving in. For short rides, comfortable jeans are fine; for longer rides, they may become a problem.
Don't skimp on warm gloves for cold weather; in any weather, cycling gloves can save your hands from being badly scraped if you ever take a spill, and the padding may make your hands more comfortable.
A thin nylon helmet liner does a lot to keep your ears warm in the cold.
Don't wear your finest clothes. Every so often, they'll get dirty as a result of biking (especially if you end up needing to do road maintenance.) A velcro cuff for your ankle can keep your pants legs from a bike grease stain (that'll never come off.) I don't recommend narrow ones -- their velcro patch is so small that they fall off easily.
Don't wear flip-flops -- wear shoes that cover your feet and can't slip off. This is an important safety issue. Your shoe slipping off when you're trying to pedal could cause an accident; in an accident, your feet could be scraped badly if they're not covered.
All of this makes it sound harder than it is. When I buy a jacket, I have its suitability for biking in mind, and I get one with vents, but it's not a biking jacket. I use the same one on or off my bike, just like I use the same gloves. Other than the helmet liner and velcro cuff mentioned above, I don't have a wardrobe particular to biking. If you already have casual clothes, odds are good you won't need one either.