Guardo el enjuague bucal en la mochila para no olvidarlo cuando viajo.

In Spanish, guardar commonly means to keep, to store, or to put away something in a place (like a bag, drawer, or closet). While guardar can sometimes translate as to save (e.g., guardar dinero = to save money), in this sentence the context (en la mochila) strongly points to the “store/keep” meaning.

Enjuague bucal is mouthwash (literally “oral rinse”). It’s widely understood in Latin America. Another common term you may also hear is enjuagüe bucal (with an accent on enjuagüe), but enjuague bucal is very common and natural.

Nouns ending in -e can be either masculine or feminine; the ending doesn’t reliably tell you the gender. Enjuague is masculine, so it takes el: el enjuague (bucal).

En la mochila means in the backpack (location where it is kept).
A la mochila would suggest movement toward it, like “to the backpack,” and would sound wrong here unless you used a verb of motion (e.g., Lo meto a la mochila = I put it into the backpack; more common: Lo meto en la mochila).

Spanish often uses the (el/la) where English uses my/your, especially when possession is obvious from context. Guardo… en la mochila naturally implies it’s the speaker’s backpack. You can say mi mochila if you want to emphasize whose backpack it is.

Para is used to express purpose: “in order to.” When the subject stays the same, Spanish typically uses para + infinitive:

• Guardo… para no olvidarlo = I keep it… (in order) not to forget it.

If the subject changes, Spanish often uses para que + subjunctive:

• Lo guardo para que tú no lo olvides = I keep it so that you don’t forget it.

Olvidar is a transitive verb: you forget something. Here, lo means it (the mouthwash), and it attaches to the infinitive: olvidar + lo → olvidarlo.

You wouldn’t use le because le is typically for indirect objects (to/for someone). Forgetting is directed at the thing forgotten, so lo is the standard choice.

No. With an infinitive, Spanish allows the object pronoun either:

• attached to the end (olvidarlo), or
• placed before a conjugated verb (if there is one).

Because olvidar is an infinitive here, you cannot say para no lo olvidar. You must use para no olvidarlo.

With cuando referring to habitual actions or general situations, Spanish uses the present indicative:

• cuando viajo = when I travel / whenever I travel.

If you mean a specific future trip, Spanish usually uses subjunctive:

• cuando viaje = when I travel (on that upcoming occasion).

Both can be correct depending on the meaning you intend.

Viajo can mean either, but in this structure (cuando viajo) it most naturally means whenever I travel / when I travel as a routine or repeated situation. If you meant “right now,” you’d more likely say:

• cuando estoy viajando (less common), or just describe the current trip directly.

The present tense in Spanish is often used to describe a habit or regular practice:

• Guardo… = I (usually) keep / I keep (as a routine).

If you mean a single completed action:

• Guardé el enjuague… = I put away the mouthwash… (once, in the past)

If you mean “I have put it away” with relevance to now:

• He guardado el enjuague… (more common in Spain than many parts of Latin America; in much of Latin America, ya lo guardé is often preferred).

Yes, it’s possible, but it shifts the feel:

• cuando viajo = when/whenever I travel (clear time clause)
• al viajar = upon traveling / while traveling (more like “when traveling” in a general sense)

Both can work, but cuando viajo is very straightforward and common for expressing a repeated situation.