I generally ask if they want me to bring something.
I have a couple of friends and every time i go their their place i buy or make a yummy cake or cupcakes etc.
DD1 went to a friend at kinders for lunch one day and we joined them so i made some mini cupcakes for the kids.

If it's a BBQ or a party i generally don't take anything but will ask if they need anything IYKWIM.