My commute is about 12 mi round trip. I go from home 3 mi > train > 3 mi work. The mornings have been cool enough that I dont have to worry about sweating much, and the train's AC is nice on the ride home. Usually I just have my lunch, work clothes, and rain jacket in my pack. If I ever get a flat I'm close enough to work or home on either end that I can walk it and figure it out from there.

As an aside, while I understand the stereotype of americans that need to buy all the latest gear and senseless over-priced junk, trying to deny the value of clothes/gear made specifically for an activity is just stupid. Speaking as someone that has spent many hours hiking and snowboarding there's nothing better than haveing layers that both keep you warm and wisk sweat away or dry off fast when you get rained on. I'm not saying you need some team jersey to ride 3 mi to work, but you best believe when I start riding 10 mi each way next month for school that I'm gonna be rocking some padded shorts.