A combat version of emergency burn would be nice. Have it do damage to the engine and take a chunk out of your CR, in exchange for greater speed.
Other items could also have a combat use. Those combat mechs I'm hauling? Why not fasten them to the hull for some emergency point defense? Jettison fuel as makeshift mines as you said, cannibalize some heavy machinery to bolster fighter replenishment, refined alloy as extra plating, promise some luxury goods/lobster/drugs to the crew if they succeed, granting extra CR.
Also, in the matter of pre-battle stuff... Can we add a system to bribe the pirates/LP that you might run across? I'd happily pay credits/goods to just avoid some fights.