Well, this is another very interesting one. In order to make it even more exciting, we'll go with a salamander. Salamanders may look like lizards, but they're actually amphibians, more closely related to toads and frogs. There are species that begin as larval forms in water, and then move onto land. We'll use one of those as a base. The Chinese giant salamander can reach can reach a size of nearly 2 meters, so we won't have to exaggerate too much. Salamanders are carnivores and will eat anything they can catch and get into their mouths. We'll work what I know about salamanders into your story line. but first, on a smaller scale, you can watch a little tiger salamander consume a worm here:
The young man is trudging along a damp, muddy area of the island. A huge salamander catches his scent and then sees him. The guy walks on, unaware he is being watched. The salamander creeps closer. When the animal reaches striking distance, it silently darts out its huge tongue and grabs the guy by the legs. The tongue is very sticky and the young man fights desperately, but cannot get away. The salamander's tongue forms a groove in the center, which causes the guy to be trapped in the middle with stcky tongue on either side of him. The salamander brings its tongue partially into the mouth. As it does so, its movable teeth fold back in the direction of its stomach, enabling it to pull more of the guy in. Throughout this, the young man remains alive. The salamander repeatedly puts it tongue out and pulls it back in, dragging more of the guy's body in each time.Though the salmander has teeth, they are used only to hold onto the prey, not to chew. The prey is gradually guided into the esophagus. As each part of the guy's body is swallowed, it is crushed somewhat by the peristalitic action of the esophagus. The salmander may ahve some trouble swallowing the boots and jeans, but has no way to remove them, so it just keeps gradually working at it. The young man will remain helplessly in terror until he goes into shock and loses consciousness.That will happen as vital organs are crushed - by the time the lower half of his body is down the salamander. The huge animal will continue swallowing him until the entire body is in its stomach.
Salamanders have an efficient digestive system, and so, this meal will be digested in just a few hours. The jeans and boots will be partially destroyed by strong digestive systems, but they are indigestible, so will be found in the animals droppings. Since this is an imaginary salamander we'll say it can digest bones in a few hours, too. Salamanders eat 4-5 times per day, so this monster will be out hunting for another meal in a few hours.