A trust-bag is the conglomeration of a trust fund kid and a dirt bag. It is a trust fund kid who pretends to be a dirt bag transient person and acts much to cliché in that role. These individuals are often seen doing rock climbing-related activities. They are unkempt, unbathed, and upon close inspection are unaffected by any of the normal things, like jobs, that are required by normal people who do not have the unquestioned help of their wealthy parents to allow them to continue in their mediocrity.
Look at that trust-bag over there digging in the dumpster for food while drinking just purchased micro-brews... what a poser.