You did not include the other part of the question but with some googling i think this answer is what you were looking for:
"to the grocery store" modifies drive. Because drive is a verb, that makes "to the grocery store" an adverb phrase.
It's been a while since I've read the book and I don't really a lot of the context, so just from this passage I would say it says he notices nice houses and other people's wealth and maybe envies them a little bit. (although you don't get that explicitly from this passage.)
