VOLUNTEER VISA

I will be going to Ireland in a week under the volunteer scheme. I don’t use the word Visa because since I am Brazilian I am not required one. However I am concerned about my entry. What documentation am I supposed to have with me at the port of entry? I am afraid of being refused entry. On my Preclearance approval letter it says I only need my passport and insurance with me but I doubt that’s all they will require. Please, what are the documents I should have with me at the port of entry? Will those suffice?

Thank you!

Passport, pre-clearance letter, insurance letter. That's about it.
They may ask you where you will be staying, who's your employer, what work are you going to do, are you getting paid. If you have paper document, print them out.

I get annoyed when queuing in the immigration line and people in front of me don't have any paper document with them, don't remember their employer/hotel/flight details etc, and have to get out their phone or open their baggage to find them out.