Ahhh , I can't stand watching the funny answer anymore !!!
I am the Thai rice supplier.
Whatever bag size contained in 1x20' container is possible.
The smallest size I have exported is 0.5 pound or 0.2 kg bag.
The maximum weight per 20' container is around 19.5 to 20.5 MT but not over 21 MT otherwise you need to pay for some extra charge.
Thus , there will be around 400 bags for 50kg bag size.