You have to keep them. I did a test, basically I brought a trap diagram/recipe, a made the trap, I then sold the diagram/recipe and when i went to make it, isn't available any more. Simply put, buy what you need at the time, do not stock up on every one you see, because even though they only weigh 0.1 when you have a lot of them, they can mean the difference of walking slowly everywhere or running.
There are a few bags in the game and 1 is specially for recipes and diagrams where they have no weight, but apparently you have to wait until mid way through Act 2 before you can find it.
Live Fast, Fight Hard. Hustle, Loyalty, Respect. by JOHN CENA (WWE Heavyweight Champion)