This was said when you bought something that you were very excited about, or received a wonderful gift, or made a major purchase. If you brought home a new coat that you loved, and tried it on to show her, along with "It's beautiful," or "It looks great on you," my mother would say, "Wear it in good health."
Another variant is, "You should wear it in good health." The you should part is a wish or a prayer, similar to the more formal (and religious-sounding) may you. It expresses a desire. In "wear it in good health," the you should or may you is understood.
Tangent: there is also a sarcastic version of you should. "Maybe the Democrats will grow spines and vote against this war." "You should live so long." This is roughly equivalent to hell freezing over.
Another tangent: there is also the Jewish you shouldn't. "Bring a snack, you shouldn't faint from hunger," meaning, bring a snack so that you won't be hungry. This is often an exaggeration meant to be humorous.
So when I recently told my mother about our new car, she said, "Use it in good health."
I've always assumed this was a Jewish-culture thing, but I actually don't know. Perhaps it's even more specific, a Brooklyn-Jewish thing. Or perhaps it's not Jewish at all, perhaps it's generational. Do you know this expression? Did your family from [somewhere] use it?
I know most people will answer on Facebook and not here. But if you could leave a comment here so it's captured on this blog, I would appreciate it.
About the saying itself, it's one of those idioms I heard without ever thinking about. With my mother now the only person in my life who would use these old expressions, I sometimes hear them with fresh ears. I love this one. It acknowledges the importance to you of this material object, and at the same time, puts it in perspective. The coat is beautiful, but only if you have the good health to enjoy it.