In J.D. Salinger's novel of teen angst, Holden Caulfield spends several days in New York before returning home to the reality of his having been expelled from school. While he is at Grand Central Station, a place that mirrors Holden's own impermanence, he watches people traverse the station with their baggage, and he is reminded of his roommate who did not have suitcases as fine as Holden, but hid his hoping that others would believe Holden's to be his, and, thus, elevate himself socially in their perception.
Obviously, then, suitcases are perceived by people as an indication of one's socio-economic class. For, Holden narrates,
The thing is, it's really hard to be roommates with people if your suitcases are much better than theirs---If yours are really good ones and theirs aren't. You think if they're intelligent and all, the other person...won't give a d**** whose suitcases are better, but they do. They really do.
So, while Holden is in Grand Central Station, he views the social strata by means of examining people's suitcases. The two nuns, who have taken the vow of poverty, have rather cheap suitcases with them, but they are unconcerned since they have given up the things of the world. Holden talks with them, but he is slightly ill at ease because he is not a Catholic and worries that they will ask him if he is. He is relieved when they do not ask him, saying his discomfiture is similar to the situation with suitcases:
It's just like those suitcases I was telling you about, in a way. All I'm saying is that it's no good for a nice conversation. That's all I'm saying.
Holden Caulfield recognizes that there are social and religious barriers among people that cannot be crossed. The suitcases symbolize these unspoken barriers.