Learn Polish: Tu jest wasz paszport i plecak. - Here is your passport and backpack.

Both mean "your", but wasz is plural—you use it when you are talking to more than one person (like "y'all's" or "you guys'"). If you were handing a passport to just one person, you would use twój instead.

If wasz is for multiple people, why is it in a singular form here?

In Polish, possessive pronouns change their ending to match the thing being owned, not the owner. Even though the owners are plural ("you guys"), the paszport is just one item, and it is a masculine noun. Therefore, we use the masculine singular form: wasz.

Does wasz apply to both the passport and the backpack?

Yes, it means "your passport and your backpack". Since both paszport and plecak are masculine singular nouns, the single word wasz perfectly matches both of them at the same time.

Since there are two items (passport and backpack), why does the sentence use jest (is) instead of są (are)?

When pointing things out with tu jest (here is), Polish often matches the verb to the very first item in the list. Since paszport is singular, the verb stays singular as jest. This is very similar to how English speakers naturally say "Here is your passport and backpack" instead of "Here are".