What to do with airport baggage on Belgian train from Brussels Airport to Brugge?

You are coming from the airport, so baggage is expected. It’s not an issue. I can’t even remember what we did a couple of ago in the same situation. I know it was neither on my lap nor out of sight.

Was there in March and there were some locations on the train that had more room for luggage. For smaller bags, there were overhead bins. We travel with smaller suitcases, 1 each, and it wasn’t a problem. Since the train was pretty empty, got were able to lace out suitcases right in front of us, and still had some leg room.

There are some luggage racks in each car, so you could secure there. I've found that the trains aren't always super full at the airport. Some of them have some facing seats with a table, so you could smoosh your luggage in with you there. If you have carry-on size, you can go to the overhead bin. I'm trying to remember what the underseat clearance is, but can't quite recall.

Also - many of the airport trains are double deckers, so you'll be going up or down a few steps with your cases.

Just a bit of general strategy here - head for the cars towards the back, as the generally have fewer people. Also, unless you really want to make the direct train to Brugge, and it's coming, don't rush. The trains do run frequently.

The airport to Brugge train had large luggage racks.
I came back switching trains in Brussels Zuid. The Brugge-Brussels had tiny racks, like for a backpack. The airport train for the short segment had large racks.
I'd go with the direct in your case.

Thank you to each of you who has posted, these are very helpful.