What I would do (my tuppence worth):
I would scrap a lot of the items you can claim tax credits or tax relief for - like work clothing, service charges, medical insurance, union subscriptions and so on - the items that can't be considered to be impacting the elderly, infirm or disabled or to be impacting job security or job creation (so not tuition fees, business expansion plans and so on).
I would get a lot tighter on the self-employed writing anything and everything off as 'business expenses'. The self-employed do not pay anything like the same tax as PAYE workers - fact!
I would scrap Rent Credit. Not just because I'm not renting anymore! But because rents are now lower than they were at the turn of the century.
I would reduce the TRS for first-time buyers from 7-years to 5-years. Anyone who got a mortgage between 2002 and 2004 does not need that support.
I would tax all foreign currency transactions.
I would bring in a two tier VAT system for Irish and non-Irish goods (say 15% and 25% respectively). If that's not legal, then EU and non-EU goods would be a reasonable substitute.
As much as I hate to say it I'd whack a carbon tax on petrol and diesel, but exempt hauliers and couriers. The end price would have to be no more than the price up North, though.
I'd possibly bring in an incentive to buy new 'greener' cars that would exempt people driving cars under (whatever) emission level from the carbon tax. That should be easy enough - a swipe card sold with the car that lets you use a different pump or something.
I would tax text messages and internet downloads - say 2c per text and 10c per GB downloaded.
I would bring in legislation to claim all unclaimed Prizebond prizes from pre-2000 and the contents of all dormant bank accounts from pre-2000. That might be unconstitutional but there could be a way around it.
I would replace all children's allowances with an An Post administered voucher system for books, uniforms, clothing and medicines and I would means test it.
I would bring in a third-level fees contribution that would be graduated on a means-tested scale that farmers (in particular) wouldn't be let screw with.
I would reduce tax relief on PRSA AVCs to 10% for everyone under 49 and 30% for everyone aged 50+ , even though that would be a bit of a kick in the stones for me.
I would treat married couples as one person for all tax assessments.
I would introduce a 4-tier tax system of 10%, 25%, 50% and 60% and adjust the bands to bring more lower earners back into the tax system, but at a low level; try to keep tax rises for low - middle income families at a minimum; start to hit people for more at around the 60K mark, then more again at about the 120K mark.