Exploration quests are all they're used for as far as I know. Had one for provisions a couple days ago, so I'm sure there are missions for all of them, just at random.
After completing mission for delivery of 10 shield generators (elite difficulty), I have received two Commodity Rewards at my ships console. After I have used them (clicked on them with my mouse) I have received:
Well,m I have just finished mission for delivery of 10 Provisions (elite). I have received 1 Common "something" as a reward. After I have used it from my inventory, I have received Console - Tactical - Phaser Relay MK II, Uncommon console, +7,5 Phaser Weapons. This comes quite handy, when you starting new career without loot from previous caracters.
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Don't know off the top of my head where to get the MkIII series.
Starbase 39 in the sierra sector has MK III and IV and I think V weapons.
1. Shield Array MkIII (Pha) - Uncommon ships shield
2. Console - Science - Graviton Generator Mk II - Uncommon common ship science console
So, use your Commodity rewards, there is no point in saving them, and Shield Array costs about 13k and requires rank Lt.Cmd.
Cya out there.
Mostly they serve no purpose anymore, aside from slight savings versus crafting them aboard your ship.
Cya out there.