Questions & Answers about Сохрани билет в кошельке, чтобы не потерять его.
Сохрани is the perfective imperative (a “do it and have it done” command). It implies a one-time action with a clear result: put it somewhere safe / make sure it’s saved.
Сохраняй would be imperfective, sounding more like keep saving/keep it safe (as an ongoing habit). In this context, you’re being told to do a single concrete action: put the ticket in the wallet.