I like the list from miketosh. For me, it depends on the length of the ride. I always take my PDM and glucose, of course. I also am sipping on gatoraide (I mix my own from powder to get it to the content I need it). For longer rides say, 50 miles+, I'll also throw into my shirt pocket an extra pod and some more solid foods (power bars are fine, but I like fig newtons). On hot rides I take an extra bottle of cool (but not ice cold) water, which I sip from but also I use to squirt the top of my head. I find that if I get overheated it makes the ride harder but I also think it effects my blood sugars.
One other thing to stress: please wear a HELMET, no matter how long the ride. You never knoww what's going to happen on a bike, and you need that prortection!