Myanmar is a tropical country. Therefore, take thin clothes. For evening, a high-necked T-shirt with long sleeves or a thin cotton sweater is handy as protection against mosquitoes. For travel in the months from November to February a warm sweater or jacket is a good idea because in the Shan State (Kalaw and Inle Lake) it can be cool. Take note that it's better to take too little than too much. What you miss, you can buy for a small amount there. If the sun is high in the sky a hat or umbrella is definitely recommended. It is wiser to spend those hours in the shade. A raincoat is handy if you travel during the rainy season. A pair of good walking shoes and some slip on shoes is all you require. Remember that the shrines of the country (even though they look like a heap of stones, as they do in Bagan) should be entered barefoot. Everyday there are opportunities to enter temples so this is when slip-on shoes come into their own. Do not dress in a 'too exposed' fashion. You had better not wear shorts. Burmese consider them ridiculous for men and shameful for women.
Important items are: sunglasses, sunscreen (almost impossible to get in Burma), anti-mosquito pen, toiletries, towel, a first aid kit, a hat, photographic or cinematographic equipment and enough film, extra batteries, flashlight, pocket knife (during flight in your hand to stop!), rope, alarm clock, stationery, books, passport with visa, sufficient cash in dollars, copies of passport and travel insurance, air ticket (s), a pass of the travel insurance that includes the emergency number, diary of important addresses , travel guide.
Possible extra items: toilet paper, tampons, reading light, universal plug. There is no need for sleeping bags, sleeping mats and mosquito nets to be carried. These are not necessary for your trip. All these items should be packed into a bag or backpack, not a hard case because it is difficult to transport. In addition, a small backpack or shoulder bag can be handy for the daily luggage. For storing valuables it's best to buy a thin money belt that you can wear under your clothes. Make sure your luggage is not heavy, more than 12 kg seems generally not necessary. At the train stations you need to take the baggage to the train/bus services yourself.