On Bare Lids
If you don't have any eye makeup on and you want a hands-free way to keep your lids clean, just slap a piece of painter's tape on your lids. Painter's tape is gentle and comes off easily, but your regular old tape dispenser variety works well, too. Just remember to let your mascara dry for about 15-20 seconds before you pull the tape off so that you don't end up marking your lids up after the fact.
To Protect Eye Makeup
If you've just created a masterwork of blending or that perfect cat-eye, you're going to want to keep your wet lashes as far away as possible. Two excellent shadow-saving options are price tags (from off your new dress, pants, etc.) and Biore pore strips (still on the backing). Both are stiff enough not to disturb your eye makeup, yet small enough to maneuver around. If you're fancy, of course, there are products specifically for this purpose, like Mascara Shields.
If you're not into carrying around rolls of tape and mascara-encrusted pore strips, guitar picks are a purse-friendly solution for touch ups on the run. They're tiny enough to go in any clutch, the shape makes them versatile to work with, and when you're finished using them, they're easy to wipe off. Plus, they come in a variety of cute colors. Some mascaras, like Eyeko, even come with a little "shield" that's actually just a modified pick.
Source: Flickr User Francesco Rachello