A "Headsweats" bandana does a pretty good job of avoiding helmet hair. I was afraid it might result in matted hair but it doesn't - and the hair stays pretty dry. The headband part can cause a little muss on the hair at the front of the head, but much better than helmet hair.
Some Nike polyester shorts - don't really have any "name" to put to them, but they are fairly soft, very flexible, have no rigidity (no creases) - work pretty well over biking shorts. I notice almost no difference between wearing them on top or not. I like having the front pockets - easier to get something out of in a hurry.
If you ride your bike to a beach and need to carry a mat, buy a "Neatsheet" (I got mine at Walmart). Separate the two plies and then cut the single ply in half. The result is a pretty darn compact beachmat that fits anywhere. I can even roll it up WITH a pair of swim trunks and fit it in a water bottle cage (usually inside a little nylon bag to keep road grime off).
I have noticed that sometimes people ask whether or not bicycle jerseys are really better than a normal shirt - they are (not to say it has to be an "officially" labeled bike jersey, but the coolmax and other materials really help a LOT. Can't believe I rode for a long time with a regular shirt.
While it may not be best for speed, I love my bicycle sandals. VERY comfortable when it is warm plus just easy to get in and out of.
Backpacks aren't a bad as I thought they would be (I use a camelback Mule with the water container removed). I did use a small backpack before that which was nothing special. Darn cheap, but resulted in heat/sweat issues where it contacted the back.