Here's a breakdown of the key issues:
* Greg's desire to be popular: He wants to be part of the "cool" crowd, leading him to make impulsive and sometimes foolish choices. This is exemplified by his attempts to befriend the popular kids, including his disastrous experience with "Cheese Touch."
* His awkwardness and clumsiness: Greg frequently makes mistakes and suffers social blunders, which further isolates him from the popular kids and often lands him in trouble.
* The challenges of school life: He deals with annoying teachers, difficult classmates, and the pressure of doing well academically.
* His relationship with his family: Greg often feels misunderstood by his parents and clashes with his older brother, Rodrick.
The climax of the book sees Greg attempting to improve his social standing through a disastrous "cheese touch" scheme, which backfires spectacularly, leaving him in even more trouble.
Ultimately, "The Last Straw" is a story about the struggles of growing up and finding your place in the world, while also highlighting the importance of staying true to yourself and valuing genuine friendships over fleeting popularity.