Walking and biking are certainly doable depending on where you are staying and where you want to dine. Not to infringe on this website or any others, a quick internet "Xcalak" search may yield a good site with maps of the hotels and restaurants and their distances.
All of the lodging is located on the beach road with some pretty big potholes so biking or driving can take some time. We've learned to just take everything in stride and savor the local flora and fauna. Rumor has it that the road will be fixed manana so you know what that means
Have a great time if you do decide to visit and please ask more questions if you have any!