Find water. Assuming that you are not near an eyeglass store and aren't able to purchase their cleaning solution, the next best thing is a little warm water. Excuse yourself, go to the bathroom, or simply go to a store and buy a bottle.
Find a piece of cloth. Do not clean your sunglasses with paper towels, toilet paper or tissue. These products are made of paper which is made of wood. They are essentially pieces of sandpaper in that at their core they are a fibrous wooden material. Find a piece of cloth, preferably cotton that is not abrasive. A t-shirt is perfect in a pinch.
Dampen the cloth with warm water. Do not saturate the cloth, but use an ample amount so that the cloth is wet to the touch.
Remove the sunscreen from your sunglasses. In a small circular pattern, wipe away the sunscreen starting from the center of the glass and moving outward toward the edge. This way if there is any residual oil that remains, it will be on the edge of the lens and will not affect your view. You'll be able to clean it later when you can get to an eyeglass store and use their solution.
