If I've made anything with a significant amount of fat (eg. a roast dinner), I pour the fat into a little bowl and leave it to set in the fridge. Once it's set it goes into the freezer (in a bag) to keep it from smelling. The next time I'm putting my rubbish out, I grab whatever collection of fat I've got (along with bones, which I also freeze) and toss them in the rubbish along with everything else. I don't know if that really helps in relation to the really small amounts that are left on cooking utensils and plates though. I'd love to hear any good solutions for that!