This is kind of on topic. Don't laugh, I learned this from a wardrobe person when I was working at CBS many years ago.
If you drop greasy food (buttered bread, a piece of salad with dressing etc.) on yourself try this. Take a piece of bread -- unbuttered and the "crustier" the better -- and rub the stain like you're using an eraser, brushing off the crumbs. Do it a few times. The bread picks up the oil and the stain doesn't get a chance to set. Especially helpful in restaurants were you usually won't have anything else handy.