If, like me, you wear contact lenses, you will at some point get something stuck in one of them while you're out and about. If you end up having to take it out, it's bl**dy hard to get it back in, minus any dust or eyelashes, without solution to wash it. Even if you habitually carry some for emergencies you're at some point going to be caught short.
Don't try and use water: it's hideously uncomfortable. And don't just keep taking it back out and putting it back in dry, and rubbing your eyes... you just make the problem about four times worse.
The thing to remember is that most of your bodily secretions are more-or-less the same. Saliva and tears, in particular, are extremely similar, barring a little more salt in your tears, and a little amylase in your spit - but neither your eyes nor your lenses are made of carbohydrate, so that's no problem. Saliva's also slightly antiseptic.
They're similar enough that I have heard of saliva glands being surgically transferred to a patient's eyes to treat conditions where not enough tears are produced (although I'm not entirely confident about my source for that, so don't quote me).
Note: Do not use this trick if you've just eaten something and still have particles of food in your mouth. Soon after brushing your teeth is probably also inadvisable, and definitely don't try this if you have any kind of infection in your mouth.
Hold your lens on your fingertip as if to put it in your eye, and gently lick it. Make sure it's still in the same position on your finger, and put it in. You will find that your vision in that eye is somewhat blurry for a minute or so, but that'll soon go. It'll help to blink a few times.