You should be ok unless you are going up north or into 'jungley' areas... Typhoid, Tetanus and Hepatitus A are recommended and they are free at the docs so have them anyway... why take the chance?...
I went to Phuket in March, and didn't take any specific jabs / pills. Water tends to be OK, but drink bottled if you want to stay on the safe-side, make sure it is sealed. Can avoid salads, ice cubes, and ice cream if you are prone to being ill. Make sure food is hot and cooked in front of you when possible.
If you go to Patong beach in Phuket, go to a place called Restaurant 6, it is on the road parrallel to the beach. There are no tourists there, only locals. The food is very good, large portions, and dead cheap. Highly recommended!!
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