The Mets have quite a few options for extensions, especially after the biggest name pieces are off the board and playing in Toronto and Los Angeles. The top of that list, obviously, is Francisco Lindor — he is 27, arguably the best shortstop in the game and a top ten player overall, and you just traded two shortstops to acquire him. They have to extend him. He is priority one.
The player who should be the second biggest priority is also likely to be very difficult to retain — Michael Conforto.
After George Springer spurned the Mets for the Blue Jays, there was plenty of discussion around how the Mets chose to extend Conforto over going all in on Springer.