An absolute phrase contains two essential components: a noun (or pronoun) and a participle with its modifiers. Unlike dependent clauses, these phrases function independently from the main sentence structure. The construction "her backpack filled with supplies" exemplifies this pattern, where "backpack" serves as the noun and "filled with supplies" acts as the participial modifier.
These grammatical elements enhance sentences by providing additional context about circumstances, conditions, or simultaneous actions. Writers position absolute phrases strategically at the beginning, middle, or end of sentences to create specific stylistic effects and emphasis.