Twelve prisons have revealed that inmates like to take a break with Toffypops and Lyons Tea, according to tuck shop sales.
Last year, a new stock management and point-of-sale system was set up in every detention facility, which cost €170,565.
For the first time it meant the spending habits of prisoners could be looked at and tracked.
Data from the system shows inmates spend an average of €675,997 every month in prison tuck shops on products including soft drinks, chocolate, toiletries and even games consoles.
Each month an average of €271,318 is spent on tobacco and cigarettes, making up over 40 per cent of sales.
Inmates also spend an average of €28,211 a month on vaping products, the Irish Mirror reports.
These were particularly popular in the Dochas Centre for female offenders, where one in every four euro was spent on e-cigarette kits and liquids.
The country’s busiest tuck shop is in the Midlands Prison, where sales of €500,814 were recorded during a period of less than four months between the beginning of last August and November 25.
Sales reports show a preference for Lyons Tea over Barry’s, with inmates purchasing 245,281 bags of Dublin-based Lyons brand compared to 159,920 of Cork-based Barry’s.
The latter was more popular in Munster, by outselling Lyons by almost three to one in Cork Prison.
In Limerick, it beat the rival brand by a comfortable margin.
Toffypops were the most popular biscuits, with 17,028 packs sold.
The Irish Prison Service has said profits are used to support inmates through the Prisoner Assist Programme Fund, hardship payments, and other services.