In the case of flight bookings, a number of airlines including Aer Lingus and Ryanair have cancelled most flights until further notice. Where your flight is cancelled, you are entitled to a choice of:
Under EU law transport companies that run ferries and cruise ships (travel operators) must resolve issues caused by cancellations. If your ferry or cruise ship departure is cancelled, you are entitled to the choice of a refund or an alternative journey. Not all ferry services have been cancelled. This means you might be charged a cancellation fee if you decide not to travel. If your departure is in the coming weeks, your tour operator may offer additional flexibility to cancel bookings without incurring a cancellation fee. This option applies to ferry crossings due to depart up to end May or mid June 2020. Dates vary, so check with your travel operator directly. If you want to cancel a booking that is for a date later in the year, normal cancellation terms and conditions apply. You should contact your tour operator directly.
In terms of accommodation bookings, this very much depends on the lockdown status at the time of the intended stay. If the location of the accommodation is still in lockdown, you are entitled to a refund. If they are open but you need to cancel, you may be subject to cancellation fees and will need to check your cancellation policy.