Adding to my earlier observations, just made a tour of Makeb as well, big chests drop Medium Satchels there. No credits in any of 9 chests opened (both small and big). Quantity of blue crafting materials seems to be between 4 and 7 pieces.

On Ilum it was just Satchel and usual random green/blue items and 0 credits. Sadly I didnt pay attention to the big chest on Oricon so i dont know whether credits were gone from this one too.

I've got Small Satchel from small chests and Medium Satchel from big chest on Ilum today. In both cases there were no credits in those chests, just satchel and usual random items. I also got "Large" Satchel (at least I think it was called that, I didnt pay attention to it at that time) from big chest on Oricon. Small Satchels contained 1 stack of green quality crafting material. Medium Satchel had 2 stacks of green and 1 stack of blue crafting materials. Large Satchel had 2 stacks of green, 1 stack of blue and 1 stack of Purple crafting materials. Green item stacks contained between 8 and 12 crafting materials, blue was 7 and purple was 2 pieces. Materials were from grade 2 to 11, various crew skills.