Well I tried a lot of stuff with the tools I had (including chopsticks) and none of it worked. Eventually when I tried overfilling with oil, I think the cap got pushed further into the inside and was never felt again. Didn't come out the drain hole when I opened that, either, so I just let it be and finished the oil change.
Car drove fine, I'm just praying it doesn't cause some catastropic transmission failure somewhere down the road. I don't know much about the composition of the parts inside, but I'm guessing they're all fairly strong metal parts, and a flimsy cap thing like that wouldn't cause damage even if it did get caught somehow. Well, I'm hoping. I think I'll bus to my exam tomorrow... -_-'
On another note, there was some kind of heavy metalic thing loose, sitting just inside the drain hole, but not small enough to fall out. It had black sludge all over it. I'm guessing it's a magnet...
Well, thanks for the suggestions, here's to living through stupidity! (drinks)