These days, there are a ton of special implements for peeling, pitting and chopping various plant parts, olive pitters being among them. Turns out, to pit an olive, you don't need a special uni-tasking implement, you just need a knife.
Photo by Rene Schwietzke.
To easily pit a whole bunch of olives without a pitter, simply take the flat blade of a large knife (or spatula, potato masher or any flat thing will do) and smoosh 'em. The pit will pop right out, leaving the flesh behind. The result isn't as pretty as what a pitter would produce, but it get's the job done and I bet you already have a knife in your kitchen.