If my friend gave me a necklace before ctbing, my heart would explode from a feeling that I was so special for someone that they decided to make a present for me before passing away, and the feeling that the person is no longer around me. I think I would cry for a straight month after that. It would be really emotionally hard to process.
But still in my opinion (from a friend's point), I would receive something from a person, rather just the news that he is not alive anymore. So the decision will always be yours, however I would suggest sending something for your closest friends. I really like the idea of a necklace, or maybe a bracelet, or something like it.