Unless you plan to eat at an upscale restaurant or go to a "club", you can wear whatever you would normally wear when out and about.
There is a lot of walking so make sure you have comfortable footwear. For summer, I'd just plan on shorts and tee.
You will find a variety of attire - evening wear (gowns/tuxes) to torn jeans and ratty tee shirt. No one even blinks at either ... just wear what you are comfortable in.
For ladies, I would suggest a purse that has a strap that crosses the body. You want to be "hands free" as much as possible. I use a Baggilini Uptown purse. The strap is wide and the purse flat enough that it will just lay on my lap whether playing at a BJ table or at the slots. I've never seen a problem with purse stealing, but you don't want to have anything that you would set down and then forget. You could use a fanny pack (LOL) and I did for many, many years -- a bit dated, but you will still see them. Most ladies will have the flat type of purse with the cross-body strap.
Have fun!