Do you think the lens are too heavy, being glass?

Glass lenses are always heavier than Poly lenses. By quite a bit actually. I teach people to Fly fish and glasses are very important to me. I've lost a few pairs to the water when they fell off as I looked over the edge of the boat ONLY due to the weight of the glass lenses. I also had a nice pair of Serengeti sunglasses that had glass lenses. They didn't last a week because the first time I bent over with them on top of my head, I went to pet a pal's doggo, they fell off and the lens shattered. ONLY due to the weight of the glass lenses. I've never had a pair of polarized poly glasses fall off my face nor hat. Poly lenses are A LOT stronger as well. They will never shatter and only get knicks when they hit something hard. After Oaklay made the Poly lenses famous by shooting a pair with a shotgun anf then handing them out to retailers to show people most all companies went to Poly lenses. Many companies do not even offer glass lenses anymore and the ONLY advantage to them is the clarity. Poly will never be as visually accurate as glass but with the quality of the new poly lenses I don't see how clarity could ever be an issue unleas the lenses are damaged. Big name sunglass companies don't offer glass lenses for many reasons!

What are the little white rubber pieces that come in the little ziplock bag with it?

Good question. I was curious at first also. These rubber pieces slide over the earpieces, you hook the very flexible rubber pieces behind your ears, and they keep your glasses from falling forward—a convenient design. They hold your glasses to your face.