Marriott offers all inclusive resort packages at ten of their resorts in the Caribbean, Mexico, and Costa Rica.  None of the Marriott resorts are completely dedicated as all inclusive resorts.

The all inclusive package, known as the Escape Inclusive package in Marriott lingo, is purchased as an add-on to the normal room price.  There are a limited number of these packages sold at each resort.  When the package is sold out, it is removed from the reservation system.  This is why some people have trouble finding the package for their specific resort and dates. 

Instead of wearing a wristband, all food and beverage is billed to your room and then anything that qualifies under the all inclusive plan is deducted at the end of your stay.  The Marriott resorts have a very specific list of what is and what is not included in the plans.  You need to make sure you are only ordering what is covered by the plan you purchased.

The additional money spent on the all icnlusive plan does not earn you additional reward points within the Marriott loyalty program.  You only earn reward points on the cost fo the room.

There are minimum night stay requirements in order to qualify for the all inclusive packages.  Depending on the resort, a four or five night stay is required.  The all inclusive plan starts at 4pm the day you check in and ends at noon on the day you leave.  Any drinks or food purchased outside of these times will be added to your room bill.

Here's a list of Marriott resorts offering all inclusive packages.