Someone looked at my 100 Uses For Cardboard Tubes post and asked what I meant by "Bag Savers" (#21). It's just what it sounds like - a handy way to save grocery bags that takes up very little space. Making these takes almost no effort at all. Just stuff a whole bunch of bags into a paper towel or toilet paper tube. Doing this saves a lot of space!
In case you hadn't noticed, though, I like to... embellish things. My plastic bag saver is wrapped with colorful paper and protected with clear contact paper. I attached it to the wall with Velcro. It's a really simple and useful little thing. I'm going to make a couple more and toss one in our emergency bag (the one we grab during fire drills) and one in the bathroom for transporting wet clothes when someone has an accident.
I suppose you could try using a wider tube, like a mailing tube, to hold more bags, but I'm not sure how well they'd stay in.
Either way, this is one of those clever little ideas that'll make the other teachers a bit jealous of your craftiness. :)