Lydia Bennet

"Well, of course you can't make a potion without them," Lydia reasoned, "but otherwise it very much depends on what you're trying to do, and one can always improvise if you haven't the correct materials. My magical education has been a bit...eclectic, I suppose, so I'm rather good at that, if I do say so myself. It's all a matter of being quite firm with your materials, I find."