I allow myself one medium sized tool box for spares / tools (beyond the CS tools). It has some wire, wire connectors, crimping tool, a set of metric sockets, some small screwdrivers, duct tape, a couple of hose clamps, hose clamp socket drivers, small metric open end wrenches (7/8 mm), fuses (new and old type), spare head lamp bulbs, heat shrink tubing, soldering iron, allen wrenches, fuel filter, and off course a quart of oil.
I just completed a 4,000 mile trip, and of the the spares I had with me, only needed to use one replacement head light lamp. I did need to do some parking lot brake bleeding once - so needed clear hose and brake fluid (neither of which I had with me).
The tool box makes me feel a little better, but inevitably you will need something you do not have. Best bet, to keep up on all the maintenance and don't let hoses and belts get too old. Also, give the car a good once over before you leave checking for loose bolts / connectors.
Alternatively, pack a bicycle in the boot. The nearest town in Ireland can't be more than 10 miles away.
Have fun,
