Packing tips? Where are you moving to, what’s the weather like there? Most likely you’ll be able to buy clothes in the US cheaper than Ireland.
Culturally speaking, the US is pretty devoid of ‘culture’, at least in comparison to Ireland. I Lived in NY, ATL, CHI, LV, DEN, PDX, SEA, VAN, TX and while each has its own flavor it’s going to depend on where you’re going but you’ll just have to try to fit in and get a feel for the local. There are certain things that take some time to get used to - guns, religion and politics being the 3 button topics at ye minute, so tread carefully. Taxes, Local accountants are pretty expensive if you have complicated returns - simple 1099 you can probably file yourself if you’re anyway familiar with personal finances…
I travel full time in the US in my camper and it really depends where you are, but yes it does come up. I feel like they’re used as bait for bigger topics - as in ‘what church do you attend?’. How someone feels about religions, guns, the environments basically tells you how they vote and whether they’re your tribe or not these days. It’s become quite partisan obviously but where the OP is moving its solidly guns and religion country.