Tips for vacation

We are going on our first vacation with our 4 year old. We are going to an indoor waterpark resort for 3 days. He was a sweet little boy until he turned 4 and now I call him Kidler. He wants what he wants and that’s what he wants. I am honestly dreading it even tho I haven’t been ok vacation in 3 years. What are some tips and tricks you all recommend to have a somewhat enjoyable time?