Assuming you want to keep the items you have, the challenge is not just what to put on the long wall, but how to unify the whole space. Maybe it's just the photos, but I see walls that lean pink, floors that lean yellow, lots of gray, very dark wood cabinets on one side of the room and nothing that dark on the other side, and bold blue plaid bedding with no other blue anywhere.

So, taking a cue from the items on your shelf unit, I put some vintage aircraft posters on the long wall that include the blue plus some pinkish and yellowish neutrals. I added dark wood valances over the windows to begin to balance the dark cabinets, and put another poster on the end of the cabinets to bring some light to that area. In this large space, I would pull the rug out from under the bed to cover the expanse of bare floor between the desk and the bed, and maybe add a bench (or even small sofa) at the foot of the bed. I changed the accent pillows and throw to white to lighten the space further and lessen the amount of gray. Lamps on the bedside tables would be nice, and also by the chair if you read there.

Some ideas, anyway . . .

Perfect place for a gallery wall of family photos--generational!!

One word - art!

a long, low bookcase with lots of art above, and table lamps. if you don't have that many books, you can do little stacks interspersed with decorative objects.

it doesn't have to be as cluttered as the examples above, it could be as simple as this: