Cheapest way would be to send a text for 30p, or a MMS for 16p (both to a UK mobile)
(I assume that Myanmar is not in the EU area.)
If you are unable to connect to a roaming network at your current location, you can use the internet to topup your airtime credit with £10.
A £5 goodybag would also reset it, but the bag would be completely wasted, whereas the airtime credit can be used later.
The full list of methods are in section 13.3 of the Terms & Conditions.