It depends on how long the delay is.
If it’s only a few minutes, the pilots will likely just return to the gate and then prepare for another standard departure. If it’s a few hours, then there is likely much more to cover.
Air crews are only allowed to work a certain amount of hours. So pilots will usually check with atc for an estimated wheels up time because if one crew ‘times out,’ the airline will have to get a new crew to take over the flight for the crew that exceeded their duty time, which can be very expensive. They also may check any restrictions on slots available at their destination airport because this can also affect their arrival, which can lead to other issues. They may also check their fuel so that if it drops below reserves they can re-fuel.
There’s a lot, and I’m no pilot but I consider these to be some of the most common :)