Help w Train from Munich Airport to Passau

RE 22 goes from the same place the S-Bahns at the airport go from.
The 42 EUR ticket for 2 is a Bayern Ticket, buy out of a machine or pay a service fee at the ticket window.
There is REWE grocery store at the airport, as well as other shops.
https://www.munich-airport.com/rewe-25406028

(1) Station page of "Flughafen München" inclding map:
https://www.bahnhof.de/en/flughafen-muenchen

In "Live departure and arrival" you can see also RE 22 listed.

(2) Yes.

(3) There are a Rewe and an Edeka supermarket in the terminal. Airport website helps localizing.

Since you did not tell us from where you are flying to Munich or the airline, I will give you a general description of where the train station is relative to the terminals. There are two terminals at the Munich airport, Terminal 1 and Terminal 2.

Terminal 1 is all in one long building and services many European airlines flights, except for Lufthansa, to European countries, example, Air France to France or British Air to the UK. Terminal 2 is another long building, but some gates are in a satellite building connected by underground shuttle trains to the main building. Terminal 2 serves Lufthansa and other non-European flights, like United to/from the US. The MAC (Munich Airport Center) juts out from the middle of the T1 building towards Terminal 2. The train station is downstairs in the MAC.

I haven't used T1 for over 20 years, since before T2 was built, and T1 was the only terminal. As I remember, there are hallways in T1 leading to the MAC and the train station. I assume there are sign showing you how to go. From T2, you walk out the front door and across a covered patio to the MAC. You should be able to see the large green circle with a white S, for the S-Bahn station from the patio. The tracks are on the lowest level. There will be a ticket machine on the platform between the two tracks. The ticket counter is upstairs.

Munich Airport > Landshut > Passau is by regional train only. There is no reason to pre-purchase these tickets - regional train tickets do not sell out and do not offer seat reservations. And there is a reason NOT to pre-purchase; a Bayern Ticket is non-refundable... you will lose the €42 if your travel plans must be cancelled or changed, or if your flight is cancelled. You can buy at a ticket machine... OR you can buy it using the DB phone app.

https://int.bahn.de/en/booking-information/db-navigator

Your Bayern Ticket is not train-specific; you can use it for ANY regional trains at ANY time on this day since it is a Sunday, whether your flight is late or on time.

Thank you all! I appreciate everyone’s clear directions and feel better about where to go upon arrival.

the fastest route is taking RE 22 to RE 3 (changing in Landshut)

In fact, the fastest route would be taking Bus #635 to Freising station (ca. 15 min.) and transferring there to RE3; it saves 15 min.

BTW

You can buy at a ticket machine.

The ticket machines are located to the right and left of the DB ticket counter in the airport center. Most people line up on the right because these are the only machines you can see when you come from the gate. Just go to the other side, where it's much less crowded.

Thank you for the great tip on the ticket machine locations!

One more thing. You should write the names of all the travelers on the back of Bayern Tickets bought from the machine.