Abans de sortir, guardaré el passaport a la bossa i estaré llesta.

Catalan often drops the subject pronoun when it is clear from the verb ending.

• guardaré = I will put away / I will keep
• estaré = I will be

So jo is not needed. You could add jo for emphasis or contrast:

• Jo guardaré el passaport... = I will put the passport away

But in a normal sentence, leaving it out is more natural.

After abans de , Catalan normally uses the infinitive when the subject is the same as in the main clause.

So:

• abans de sortir = before leaving / before going out

This works because the person who will leave is the same person who will put away the passport.

If the subject changes, Catalan usually uses a different structure, for example with abans que:

• Abans que ella surti... = Before she leaves...