This is really hard for me, cos I'm a crisp addict, but I've stopped eating single serving packs of crisps and just buy one big bag every week or so, so at least I only have one plastic bag to put in the bin, rather than all the little bags and the multipack bag. Mums in charge of the shopping, I don't usually go with her (becuase I'm avoiding someone who works in the supermarket she likes to go to lol!) so she doesn't have me there reminding her not to buy multipacks, but she's getting the idea slowly. I've also been making my own popcorn, yummy and you get so much out of one bag!
EDIT - Mrs Green of My Zero Waste has found a way to reuse/recycle crisp packets for charity - see here and here. I'm going to keep trying to reduce the amount of crisp bags I use anyway, because they're plastic and don't biodegrade and are made from weird chemicals, but I'm not about to give up crisps (I'm already vegan and allergic to soya and a picky eater! I need to leave some food groups I can eat!) so, for those I do use this seems an excellent solution! Yey!