Amulets are on the border between practical Kabbalah and an external manifestation of Kabbalah, such as name calculation. There is a source for amulets in the Torah. When a great sage writes Holy Names, (without pronouncing them) on parchment and puts it into a container which is worn by the recipient, it can possess healing and spiritual powers. At the beginning of the Ba'al Shem Tov's life, since he was a healer, he used amulets. Sometimes the amulet works because of the faith of the recipient in the spiritual power of the amulet. At the end of his life, the Ba'al Shem Tov never wrote the Names of God, only his own signature, Yisrael ben Sara or Yisrael ben Eliezer. This was the ultimate amulet given by the Ba'al Shem Tov.
We know that the Rebbe of Lubavitch gave dollars to people for the sake of charity. He gave an actual physical gift, but it was connected to the spiritual mitzvah ("commandment") of charity, in the merit of which blessings could be effected. The Sages teach us that whoever receives a coin from the hands of Job (a tzaddik) receives a blessing. This is the source in the Talmud that receiving a coin from a great tzaddik brings with it a blessing. Thus we see that there are amulets that are permissible. The determining factor is the righteousness and intentions of the person giving the amulet.