Volunteer for things that teach you something. Skip the ones that only make you look busy.

Not all extra work pays you back. Some of it leaves you with a skill, a reference, or a few people who now know you can be relied on. Some only consumes a Saturday so that somebody else can tick a box, and that kind is attractive precisely because it is easy to agree to and feels virtuous. Busy and better off are different states.

Ask what you will be able to do afterwards that you cannot do now, before your name goes on the next sign-up sheet. If the answer is nothing, pass it to somebody who needs the hours.