Short answer: less than people hope, and the walk into town is not the good idea it looks like on a map.
Inside the gate. The terminal village itself: shops, bars, restaurants, restrooms, ATMs, wifi. Ten to thirty minutes of your life.
The International Pier, a few hundred metres north along the road. Easy on foot, flat, and worth knowing about because of the tour-meeting-point problem.
A small number of beach clubs and dive shops immediately south along the Costera Sur, within a fifteen-minute walk. These are the nearest swimmable water to the ship, and the reason a handful of passengers never take a taxi at all.
San Miguel is not walkable in any useful sense. It is about three miles up the road, which is an hour on foot in tropical heat along a coastal highway with intermittent pavement and no shade. People do it. Most of them regret it, and all of them could have paid a fixed zone fare instead.
Chankanaab is ten minutes south by cab. Mr Sanchos, Playa Mia and Paradise Beach are fifteen to twenty-five. Punta Sur is around thirty. The east coast is forty-five and up, and is a jeep or a tour rather than a taxi errand.