The Halacha permits wearing items that can be regarded as clothing or jewelry. The Poskim grapple with the question whether one is allowed carry an item that is essentially a functional accessory, but was transformed into an ornament. For example, may one wear a gold or silver plated house key as a necklace or tie clip into the public domain? The Shulhan Aruch (Siman 301) brings two opinion on the matter. The "Stam" (unattributed ruling) states that it is prohibited because of "Mar’it Ayin." Outside observers are likely to misunderstand and view the key as a functional item and not as a piece of jewelry. The Shulchan Aruch then cites "Yesh Omrim" (Those who say) that it is permitted. Hacham Moshe Halvei (Israel 1961-2001), following the general principle to accept the Stam (unattributed opinion), is stringent in this matter. The Ashkenazim are lenient, following the ruling of the Magen Avraham, the Elya Raba, and the Mishna Berura.
It is interesting to note that Hacham Baruch appeared to be lenient on this question. Many times, we saw him wearing an ornamental key as a tie clip on Shabbat in Brooklyn. While it is difficult to assume that he ruled against the first opinion of Maran, it is quite possible that he followed the lenient "Yesh Omrim" in conjunction with relying on the Brooklyn Eruv of the Ashkenazim. While many people did not rely on that Eruv to carry in an ordinary fashion, it could be relied on while wearing a key tie clip.
Obviously, buttons on a shirt are an integral part of the shirt and do not pose a problem of carrying. However, the Poskim deal with the question of reserve buttons, often sewn onto the bottom of the shirt. Hacham Ben Sion rules that one must remove the buttons from the shirt before going out in the public domain. On one hand, these buttons are not ornamental, and on the other hand, they have functional significance and are not Batel (subsumed) to the shirt. Hacham Moshe Halevi (Menuhat Ahahva Vol. 3) disagrees, and cites proofs that the buttons are considered part of the shirt, even though they are not being used. Hacham Ovadia in Yalkut Yosef (Shabbat 2) concurs with the lenient position, although he concludes, "Hamachmir Tavo Alav Beracha"-it is praiseworthy to be stringent.
The Halachic definition of a garment is clothing used to protect the body. However, a garment or apparatus worn to protect one’s clothing is not considered a garment and may not be used in the public domain. The Shulchan Aruch brings the case of wearing an apparatus on one’s body to prevent bodily emissions from soiling one’s clothes. In our day, this question applies to wearing a protective nylon covering over one’s hat. The purpose of the covering is to protect the hat from rain, and therefore Hacham Ben Sion prohibits it. Hacham Moshe Halevi, is lenient, arguing that since it is designed specifically to fit the hat, it is considered part of the hat. All would agree that it is prohibited to wear a plastic bag or towel over one’s hat to protect it from the rain. With regard to wearing rubbers over one’s shoes, there is more room to be lenient. The rubbers serve not only to protect the shoe, but also to prevent one’s feet from getting wet.
It is prohibited for Sepharadim to wear an ornamental key on their clothing, unless there are additional extenuating factors, such as an Eruv that ordinarily one does not rely on.
There is room to be lenient to leave the reserve buttons sewn to the bottom of a shirt.
There is room to be lenient to wear a special protective hat covering and rubbers on the shoes. However, it is prohibited to wear a plastic bag or towel over one’s hat.