Hiking, painting, 3d printing, board games, gardening.
Collecting and restoring knives.
Whatever you feel like doing...
But find something that's different enough than your future job.
I mean... I troubleshoot network stuff for a living and coming home and doing puzzles would absolutely suck, as it's the same kind of stimuli (finding patterns).
Every job is different, and I burn out of different hobbies depending on what job I'm doing.
BRB, Resurrecting the aftermarket radio.
Between this bullshit and touchscreen-only controls, I've ruled out quite a few models.