Translation:I want to buy a bag of rice.
What is the difference between 一包 and 一袋? Are they used i terchangeably? Is 一袋米 correct?
一包 and 一袋 are actually the same. They both mean a bag of something. 一袋米 is correct.
Bag isn't really the right word. 包 is usually translated as bundle or package or something that's wrapped.
Yeah, Mandarin seems to have a lot of double words for things. 米饭 is also a word for rice.
I don’t know for sure but my experience is that 米 tends to be when you’re dealing with the grain (or ingredient) and 饭 when you’re eating it (cooked). 米 always seems to mean rice whereas 饭 can be used to just mean food (generally prepared/cooked food).