Can a tefillin bag become a tahsmish d’kedusha if it was not previously designated as such?

A bag which was not designated for tefillin and is only occasionally used for them does not become a tashmish d’kedushah. If a bag was previously designated for tefillin or is used for them on a steady basis, it is classified as a tashmish d’kedusha. In a case where there was no clear designation originally, the steady use of the bag as a tefillin bag is like a designation.

סימן מב, סעיף ג וס"ק כד

Can a stipulation prevent a tefillin bag from becoming sacred?

If one expressly stated at the outset that he reserves the right to remove the tefillin from the bag and store mundane items in it instead, it does not become sacred even if it was used many times. If the bag had been manufactured—or even improved--for the purpose of tefillin, however, a stipulation cannot prevent it from becoming kodesh. As soon as it is used for tefillin once, it becomes sacred.

סימן מב, ס"ק יד ו־כד וביה"ל ד"ה צר; ביאורים ומוספים דרשו, 36

Can money be stored together with tefillin?

As we have learned, there are various scenarios in which a tefillin bag does not become kodesh and may be used for mundane purposes. Nonetheless, the bag should not be used to store non-kodesh objects while the tefillin are inside it. If someone wants to put money together with his tefillin, he should prepare a separate pouch that can be carried alongside his tefillin bag.

סימן מב,ג, ס"ק כו וביה"ל ד"ה זוזי

• A mitzvah object (such as an esrog, shofar or schach) may be used for a mundane purpose. Even if it was only created for the sake of the mitzvah (e.g. a dedicated schach mat), it may be used before and after the time of the mitzvah.

• Sifrei kodesh or written papers which contain divrei Torah are considered kedusha objects and may not be used for writing mundane matters. They may not be placed directly on the floor, either.

• As we have learned, a kodesh object may not be repurposed for a matter of less kedusha. If a person stipulated at the time of the original designation that he may choose to downgrade the item to a lower kedusha, doing so is permitted.

• When must tefillin be removed?

• When can tefillin be brought into the bathroom?

• When should the straps of the shel yad be unwound?