If you were resident in Ireland you will not be able to reclaim any tax, except in the year you leave, if you have not used up your credits etc for that year.
In the year you leave, complete a Form P50 and send it with your P45 to the tax office.
PRSI - you will not be able to reclaim PRSI unless you have paid more that you should, which would not generally arise unless you had 2 jobs or something like that.
Re your pension contributions - speak to your pension provider, although normally you can only reclaim these if you are working less than 2 years.