Environmentalism sometimes runs hand in hand with frugality, and reuse is a basic idea of either. And it can also be fun and creative. So, just a few quick ideas...
Plastic shopping bags can be used to line small garbage cans.
Empty plastic coffee containers can be used as canisters to store flour, sugar, rice, pasta, beans, and almost any similar dry staple, which also keeps some pests out of them.
Empty peanut butter jars or vitamin bottles can be used to store herbs, spices, teas, small amounts of grains or beans, loose change, batteries, and kitchen or bathroom odds-and-ends like twist ties or hair bands or combs.
Empty jars and yogurt containers with lids, and empty margarine tubs can be washed and used for food storage, or as cheap semi-disposable lunch containers.
Envelopes from junk mail, blank sides of junk mail, and misprinted or old (non-confidential) documents can be used as scrap paper (my mother wrote hundreds of grocery lists on old envelopes).
Line an empty plastic coffee container with a plastic bread bag, and you have the perfect arrangement for collecting smelly food scraps and other things to go into the garbage if you don't have a garbage disposal.
Oh, and turn a few of those bread bags inside out, wash them, then save them to use for homemade breads or to wrap messy things up in, etc.
Ziplock-type bags can also be turned inside out and washed for reuse, as long as you didn't use them for meat or something else that might be risky in food handling.
Obviously this list could go on, but how about something more creative? Have an old pair of jeans with a ripped knee or seat or worn inner thighs, but still has good, sturdy fabric in the lower legs? If the hems are still in good shape, cut the legs off below the ripped knee, cut out the inner seam on each leg (but leave the french felled outer seam intact). Sew the two leg pieces together, then sew the knee end closed. The original hem of the jeans now becomes the top hem of a bag. Attach a handle (I use cheap strapping I buy at the sewing store, but you can make a strap from other jean material), and you have a sturdy, attractive tote or shopping bag for the work of cutting, three seams, and the handle. I've made a lot of these over time, but almost all of them have been "acquired".
A variation on this is to cut the legs off if the torso part is in good shape, sew the bottom closed, and add a strap for a novel bag, complete with 5 pockets (if they're this type). You can also make a purse out of a single leg. You can do these with any sturdy, non-stretching pants fabric. But none of these work well with the cheap, over-washed jeans that are so popular now, the fabric is too thin, and intended to rip and wear out quickly.
Which leads me to my thought for today. Truly good quality that lasts a long time is worth the money. High quality pants that look good for 5 years (and I have pieces that look fine after 10), even at $80, are less than half the cost of pants for $20 that have to be replaced every 6 months (10 pairs X $20 is $200). Just be sure you're paying for quality and not for the label. I can get old-fashioned heavy denim jeans for less than $30 that will outlast 10 or 15 pairs of the cheap thin ones at $15 to $20. And then get shopping bags or quilt fabric out of them...