For a weekend, you definitely need to prioritize! Skip the hourly show of the Astronomical Clock—it’s underwhelming, just see the clock itself and move on.
To save time and see a lot at once, I’d suggest a 1-hour panoramic river cruise. It’s a great way to "check off" the visual list of landmarks (Castle, National Theatre, bridges) while resting your feet and having a drink. It’s very efficient for short trips. You can read more about the short cruise durations to fit it into your tight schedule.

For food, avoid the main squares; go two streets back for better prices and taste. Try "Svíčková" or just fried cheese. And instead of the Prague Card, just walk or use Uber/Bolt, the center is compact enough. Don't miss the view from the Old Town Hall Tower—there's an elevator, so it's quick! Have a blast!