Can I go on holiday overseas while on dialysis?

Possible. If you are an in center patient, travel becomes more difficult but not impossible. Depending on where you are traveling the social woker must arrange for a dialysis center to perform dialysis at your destination location. This requires 3 week advance notice, but many dilaysis patients have been to the caribbean and mexico.
Hemo or PD? If you are on pd you should ask your center to arrange for the bags to be delivered where you are going. For hemo it is a little more difficult. You should call centers in the country you are going and ask about availability and cost. Always ask your nephrologist!