The difference in meal isn't intended to specifically prove a wealth gap between Jimmy and Bill. It helps paint the difference between Jimmy and Bill, especially in regards to quality of life.
Jimmy may complain about his life/career, but when you compared the freedoms he has as an independent lawyer to the life of a public prosecutor, you can't help but think that Jimmy's focusing on the bad (not being as rich or successful as Chuck/Howard) more than the good (having it better than Bill).
Bill is an ex-colleague of Jimmy. The main goal of the scene is to show you the difference between past Jimmy and present Jimmy. Bill is merely a representative of what Jimmy's past looked like.
The scene is short, so Bill's character is explained in broad strokes:
- Incredibly busy job, daily grind.
- Unrewarding clients.
- He can't do better than a bag of chips for lunch. Notice that this isn't necessarily a financial obstable for Bill. There are other reasons for this:
- Bill has so many cases that he doesn't have the time to go out for lunch and instead has to settle for the nearest vending machine.
- Much like his career, Bill's food habits are unhealthy and mismanaged. He never aspires for something better. Maybe he complains about his life, but never truly takes action to fix it.
- Money can also be an issue here, but it seems unlikely to be the sole deciding factor here.
To paint the picture more explicitly:
Effectively, Jimmy's holding a burger, begrudgingly looking over (in his mind) at Chuck and Howard who are having a nice steak for lunch. Why does Chuck/Howard get to have a fancy lunch and he only get a burger?
However, behind Jimmy is Bill, who is holding a vending machine pack of chips, begrudgingly looking over at Jimmy who's having a nice burger for lunch. Why does Jimmy get to have a fancy lunch and he only get a bag of chips?
Jimmy is a flawed man. We know this because we know where he ends up in Breaking Bad. Jimmy doesn't make the right choices, and Jimmy doesn't make it big in the end. Just like Walter White, Jimmy will make the wrong choices for (what he thinks are) the right reasons.
This scene is one of the red flags that shows you one of Jimmy's flaws. He's so fixated on others he competes with (Chuck/Howard), that he completely forgets that while he's not as successful as Chuck/Howard, he's still more successful than he was in the past.
This effectively mirrors Walter White's flaw. When he reached the initial goal (getting enough money for his family), he then started competing with other major players because he wanted the territory and fame that comes with being a kingpin. Jimmy is on a similar quest for greatness and forgets about the things he's already achieved.