Traveling internationally for the first time & have some questions.

I am taking a carry on & a checked bag.

I understand that my checked bag has to be no more than 50lbs & that liquids have to be smaller than 3.4 oz & for in 1 zip lock bag.

Questions:

1) For the liquids, does the size matter for liquids on my checked bag too? Or does it only apply to my carry on?

2) Will I be able to take snacks & a closed water of my own onto the plane?

3) what are your must haves for a carry on? In mine, I currently have my iPad, sunglasses, cough drops, airpods, earbuds, passport & ID, wallet, camera, pads, wipes, sanitizer, portable charger, & glasses. Is there anything else I should take aside from this?

4) In my checked bag, I have my clothes, footwear, bikinis, undergarments, makeup, skincare, & hair items. Is there anything else I should take with me aside from this?

5) Also, are there any special tips or suggestions you guys would recommend for me as it being my first time on a plane? To make the process easier & things to keep in mind & watch out for?