My friends are annoying me but I don't want to be rude?

Lately I have realised how negative some of my friends are, like they will always find something to complain about and it's beginning to annoy me a lot more than it used to.
Especially when my friends all have small families therefore are a lot more privileged than me who has quite a large family, therefore I am used to non-branded things such as primark and charity shops but my friends always are on about ted baker, Ralph Lauren, topshop and other expensive places. When they all talk about shopping it makes me feel left out as I can't afford those things and prefer the cheaper things.
I don't really know what to do as I can try hanging around my other friends but am beginning to feel left out with them as they have more private jokes, I also don't want to be rude to my friends because I have told them many times how I feel.
Any advice????