It's raining and you are in Phuket Town without anything to protect you from the rain! Well there are a plethora of coffee shops in Phuket Town which I have visited and these prove to be a welcome find when you get caught in a rainstorm.
However there are also a number of places that you can buy all the bits that you might need.
A bag for all your bits
A poncho in many colours.
And there are always more things that you can find...