Not really a mod but an add-on like the corkscrew screwdriver, so I thought it would fit best here.
I just discovered that the hook that comes on many 91mm models actually has enough spare room behind it to securely store a needle and thread. While other tools will not close properly with anything behind them, the hook will, and is thick enough to secure it properly.

Closed, without needle inserted:

Closed, with needle inserted:
