1. well let's get the obvious one out of the way- use it as eyedrops! i do this when i have to get up at an ungodly hour to work at an estate sale at 7 in the morning.... and also in the afternoon when i inevitably get sleepy and bleary-eyed....
2. dab it on pimples or red spots. eye drops don't just get the red out of your eyes, they take it out of your skin too. i do this a lot when i go swimming and can't wear lots of concealer. just put it on any red spots on clean skin and leave it, or put on makeup after that. it makes your skin tone more even.
3. use it to mix liquid liner. last week i was just piddling around at home, and tried to wash my hands, and the water wouldn't turn on! the maintenance guys were working on the plumbing. oh, the joys of living in an apartment.... but it was one of those days where i *really* needed some eyeliner. but somewhere in the deep recesses of my cognition, i remembered reading that you can use visine (instead of water) with dark eyeshadow to make eyeliner. perfect! that's so genius, because visine is formulated for eyes, so it won't irrate them as eyeliner! and it worked great!
so recently, i've just permanently kept a bottle of eyedrops in my makeup bag. it can really save the day.