A girl that bring her bestie with her when she goes for a date with someone in a public place indicates the lack of trust (unless her bestie is nosy and wish to be involved).
I can tell you to just act the way you are, it’s clichè, but it’s true. What you need to wear? Well, that depends on what you like to convey to them. If you’re athletic and play basketball you can wear your sport shirt, especially the sleeveless ones, girls like guys who play sports. In general you can simply wear a neutral color (white, black, or grey) jumper and complement that with jeans of relevant shade, black and blue would be nice. You want your appearance to describe who you really are or what you’re doing in your life so to not giving her a false impressions, first impression is important, and some girls have expectation in what their potential partners should be like and may subconsciously judge you based on your appearance alone even though the general rule is to accept you the way you are. Don’t forget that a nice hairstle (unless you’re wearing hat, etc) is just as important too. If you look decent/cool and smell OK then you’re good to go.
Where to eat? Since they’re probably new to your town they’ll expect you know how to show them around the area, and this include introducing them to your local delicacies. Pick a well known local eatery that is affordable, has nice environment, and a place that won’t be too crowded at the particular time when you take them there. You can ask first what type of food they like to eat then decide the place. If they say it’s up to you then take them to your recommended place. Don’t pick messy food to eat, and certainly no food that makes your breath smelly. After you all have had your lunch and if there’s still a lot of time you probably want to take them to play around the town, or at least walk around the town to introduce them to some of the local entertainment or facilities over there and see/ask them if they want to try.
All in all, just enjoy your time, don’t think too much about it, and treat them like you’re going out with your cousins or new friends. Good luck to you.