A mojo bag can be used for any reason (within reason), they must be carried around on your person for a set amount of time and must be fed weekly (or so), in order to keep them "alive", they are not meant to be seen but if they are touched by anyone other than you they are deemed "dead" and will no longer work. Mojo bags are very slow acting, often taking months to take effect.
A witch's bottle is usually for protection and drawing negativity, used as a decoy to avert negativity away from you and into the bottle (though I could be wrong), they are not kept on your person and can be placed where it can be seen (unlike mojo bags), they are often fast acting, as soon as they are completed they begin their work.
I hope this helps somewhat.
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