Drippings: The next time you make a roast, scrape the drippings into a glass jar or bowl to keep in your fridge. Make sure you scrape out all the bits and pieces, especially the browned bits, since these will lend a lot of flavor. When you go to use it, the fat will have mostly congealed. If there is a thin layer of transparent, liquid grease on top, you can skim this away. That will be any other vegetable oil you used in your roast. The rest of what is in your jar will be in two layers. On top will be the fat from the roast, and on the bottom, darker, will be the gelled juices. I like to give it a good mix, and use a bit of both. The juices will reduce, but lend a lot of flavor, kind of like very intense broth. Also, remember, this will probably be salty, so season your vegetables accordingly.