Yes.
From the third book:
The very first time we're introduced to Lupin, the description emphasizes how poor he looks:
The stranger was wearing an extremely shabby set of wizard’s robes that had been darned in several places. He looked ill and exhausted. Though quite young, his light brown hair was flecked with gray.
[...]
“It’s on his case,” she replied, pointing at the luggage rack over the man’s head, where there was a small, battered case held together with a large quantity of neatly knotted string. The name Professor R. J. Lupin was stamped across one corner in peeling letters.
Harry Potter and the prisoner of Azkaban, chapter 5, "The Dementor"
And it's not better by the time of the Sorting ceremony/Dumbledore's first speech:
Professor Lupin looked particularly shabby next to all the other teachers in their best robes.
Harry Potter and the prisoner of Azkaban, chapter 5, "The Dementor"
Later on, Lupin being a great teacher, the only attack point that Malfoy has on him is his poverty: (note: agreed, since it's coming from Malfoy, it's exaggerated into belittling Lupin)
“Look at the state of his robes,” Malfoy would say in a loud whisper as Professor Lupin passed. “He dresses like our old house-elf.”
Harry Potter and the prisoner of Azkaban, chapter 8, "Flight of the Fat Lady"
As reminded by Aegon in the comments, he might have had to skip some meals:
He was as shabby as ever but looked healthier than he had on the train, as though he had had a few square meals.
Harry Potter and the prisoner of Azkaban, chapter 7, "The boggart in the wardrobe"
There are possibly a couple of other mentions of his shabby robes in the book, but the previous examples are pertinent enough for this one.
From other books:
Well Lupin describes himself as poor. When trying to shut Tonks off:
“And I've told you a million times,” said Lupin, refusing to meet her eyes, staring at the floor, “that I am too old for you, too poor... too dangerous...”
Harry Potter and the Half-Blood Prince, chapter 29, "The Phoenix Lament"
Also, it's hard for all werewolves, due to the acts of kind, tolerant, open-minded professor Umbridge:
“I know she’s a nasty piece of work though- you should hear Remus talk about her.”
“Does he know her?”
“No, but she drafted a bit of anti-werewolf legislation two years ago that makes it almost impossible for him to get a job.”
Harry Potter and the Order of the Phoenix, chapter 14, "Percy and Padfoot"
From Pottermore:
Well Bellatrix beat me to it. See the beginning of her answer :p
From interviews:
In this interview, JKR states that James lended Lupin money on a regular basis:
Jo related the fact that Remus Lupin, prior to the third book, was unemployable because he was a werewolf and upon his graduation from Hogwarts along with James and Lily, was supported by James using their own money.
J. K. Rowling at Carnegie Hall
EDIT: as for having chocolate on the train, Bellatrix's answer is once again quite complete, though I'd add this quote:
“Well, he should have some chocolate, at the very least.” (note: Madam Pomfrey)
“I’ve already had some. Professor Lupin gave me some.”
“Did he, now? So we’ve finally got a Defense Against the Dark Arts teacher who knows his remedies?”
Harry Potter and the prisoner of Azkaban, chapter 5, "The Dementor"
That certainly shows that Lupin took chocolate precisely for this situation. He might have had some chocolate on him just because he liked the taste of it, but it doesn't feel like his character. And, he's quite poor to begin with.