Aran Islands

I'll be anxious to see other answers also. We will be going to the Aran Islands in June also and I heard pre booking wasn't necessary that you could purchase your tickets the day before at the ticket kiosk in town.
We are staying close to the main drag so that's what we had planned to do. Were not riding the bus to the ferry we are driving our car so weren't to concerned about pre booking.

Jim Wilson

You can buy your tickets the day of by just showing up a few minutes prior to the ferry leaving.

We unfortunately were unable to go last year due to weather but have heard great things.

We opted to get our tickets two days ahead once we felt sure that the weather would cooperate. It was easily done on line (while we were having lunch in Dingle). That said, there were plenty of walk ups the day we made the trip--they had no problem getting tickets. It was mid September--I don't imagine early June would be much different.

We want to plan around the weather so it's nice to know we can wait till arrival to purchase tix, thanks!

The weather forecast goes for more than just the ferry ride. It can get pretty breezy along the spine of the island - might need to reconsider the bikes if it gets too windy. That said, it is a pleasant place to bike around on a pretty day - not much vehicular traffic aside from the small tourist vans that are available at the ferry landing and the occasional jaunting cars that will be plying the same route out to the fort and back.

Bikes are a good way to go; the traffic is mostly the tour vans. I don't do many tours, but for the islands, I did pick one of the tour vans that are available as you exit the ferry. It was fun, and the guide was entertaining, with stories about growing up and living on the islands.

The disadvantage is that you arrive at Dun Aengus along with almost everyone else.