score:3
The consensus online seems to be that, at the time of writing, there are no luggage lockers around Yangon. Your best bet would be to ask a hotel to keep the luggage for you. They will most probably ask for a fee. Even better would be to leave your luggage in a hotel where you plan on staying once you come back to Yangon, if applicable. Other options include hire a car with driver for the day and leave the luggage in there, and leaving your luggage at the bus station ticket counter. Both options will cost you.