Small - Below Human size
Medium (S) - Human size and up to the size of a small horse.
Medium (M) - Horse sized to the size of a large SUV.
Medium (L) - The size of a Tank
Medium (XL) - the size of a monster truck.
Large (S) - the size of a one story house
Large (M) - the size of a two story house
Large (L) - the size of an Olympic swimming pool
Large (XL) - the size of a football field
Colossus - the size of a golf course.
Depending on the size of the creature numerous materials can be harvested from it to make equipment and other things which can aid your survival, likewise hunting creatures for food is a worthwhile option as their flesh is usually more satisfying in terms of stamina replenish than fruits and nuts, unfortunately when not preserved just like fruits they rotten and when bloody they can attract predators and other scavengers by scent.
Small Creatures have 5-15 Scavenging Materials
Medium have 20-30 Scavenging Materials
Large have 35-45 Scavenging Materials
Colossus have 50-60 Scavenging Materials.
When harvesting materials from creatures one still uses the chance of success however there is more leeway than normal scavenging for gaining resources this way.