I tend to have a pair of prescription sunglasses in my bag in a hard sided case which also can serve as a backup pair of glasses.

Also, get fited for contacts and keep a pair of the disposable lens in your bag. They don't take up much space, but are a complete spare. Make sure you protect them so the plastic "foil" doesn't get punctured. One approach is to tape them foil sides together. The only downside of this is that you need clean hands to be able to put them in.

On the duct tape front, a while back my wife's shoe busted open while we were at a park. A quick wrap with duct tape from by bag insured minimum hassle.

-john