Normal stuff you can find:
Ammunition types: MCB-25 / MCB-50 / SAB-50 / UCB-100 / RSB-75
Rocket types: PLT-2021 / PLT-3030 / HSTRM-01 (Hellstorm) / UBR-100 (Hellstorm)
Mine types: ACM-01 / DDM-01 / EMPM-01
EMP-01 (burst), Log-disks, Xenomit, Jump Credits, Galaxy Gate Energy (spins), 1 hour boosters.
Rare stuff:
CLO4K_XL CPU (50 charges), G3N-7900, SG3N-B01, SG3N-B02, LF-2, LF-3, LF-4, Vengeance Design, Goliath Design, 10 hour booster, APIS Blueprints, APIS drone (fully built).
I think someone did a test on the english forum, he used 1500 keys and he calculated that the he had 0,3% chance to recevie one. It's all random but i think it's around 0,1% to 1% recieve one.