The use of the backpack to remind Samuel of his struggles is an example of symbolism.

Here are the answers to your questions:

1. The use of the backpack to remind Samuel of his struggles is an example of symbolism.

   • Answer: $\boxed{\text{Symbolism}}$

2. The figure of speech used in the extract "Her voice piercing the noise like thunder clap" is simile.

   • Answer: $\boxed{\text{Simile}}$

3. The literary device found in the word "rustling" (referring to the sound of leaves) is onomatopoeia.

   • Answer: $\boxed{\text{Onomatopoeia}}$

4. The statement "The vibrant colours of flowers on trees seemed to mock Abigail's sorrow, her beauty a plain difference of her inner turmoil" uses personification (flowers seeming to mock) and juxtaposition (contrast between external beauty and inner turmoil).

   • Answer: $\boxed{\text{Personification}}$