Han's fancy new jacket has plenty of pockets.
What are these things?
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Page 46 of the visual dictionary shows this picture:
While nothing states that what he has in his pocket are the detonators, the tip of what's poking out of his pocket closely resembles the bottom of the detonator (seen on the left hand of the page).
Further evidence that they're not fuel cells for the blaster are on the same page, where the fuel cell labelled is a cuboid.
Further, the only similar item I can see on 'modern' resistance pilots are signal flares, seen on Snap Wexley's leg.
On the older uniforms, the arm patch does indeed hold data cylinders (and safe passage documents for downed pilots) :
I presume pilots no longer need safe passage documents nor data cylinders. They also probably don't need detonators, where a guy like Han would.