Loot Chests can be found on most Planets and in Towns. Their content is based upon the level of the area you are in. Generally, however, opening them will always reward you with Credits, Scrap Metal, and Loot. Sometimes they will also give Health and Mana Packs or Combat Chips. Loot Chests are the only source of standard Rings, which have a 1/20 (5%) chance of appearing when you open one.
There are two kinds: Blue and Gold. Blue chests are more common and appear on most hostile planets and in Towns. Gold chests, found in large quantities on Plaguelands and The Whisperwood planets, rarely appear where a blue chest would normally spawn on most other hostile planets; to compensate for their rarity, they reward you with more Credits and Scrap Metal. (Whether they also give more of the other rewards as well is still being researched.)