Nowadays, it is not very difficult to buy necessary things in Myanmar especially in Yangon. There are many new and big super market everywhere in Yangon where you can buy most of the things easily.
But for some specific and personal things, I would like to advise you to bring together with you if it is not too heavy. It will save your money and also available to you when you are in need. Frequent electricity cut out is common in Myanmar even in Yangon, so it is wise to bring a small torch with you.
Here, I create infographic for necessary things you should bring when you come to Myanmar.