This will not be a very long post. One, I am short on time this morning and two, there really are only 2 options for this posting - reusable containers and reusable bags.
Reusable containers - Reusable containers can be made out of just about anything - BPA free plastics, aluminum, stainless steel. They are relatively self explanatory, you fill them, then your child brings them home and you wash them and reuse them the next day. There are insulated options as well for things like soup, but I will talk about those when I address water bottles and the like. I do not currently use any containers, but I am thinking about investing in a few of these for things like strawberries (Sum's fave) and other things that get smashed or crumbled easily. In my last post I talked about the containers that come in the Bento boxes. Those are great as reusable containers as well, but make sure you are getting the ones that come with lids.
Reusable sandwich and snack bags - With the addition of these bags to the girls' lunches earlier this year, we became totally plastic free in their lunchboxes.
These are made by snackTAXI and I bought them in both the sandwich and snack size. They are machine washable, and I have successfully washed peanut butter, jelly, honey, and mustard out of them. I take them out of the kids' lunches and turn them inside out at the end of the day to get all the crumbs out and then we are ready to go for the next day. There are a couple of other companies, ReUsies and Lunchskins, that make similar products.
Another option that is widely available in retail stores are Wrap-N-Mats. These are great, especially of you are using reusable containers. I don't have any experience with them, but I was thinking about getting one to use in Den's lunches since his sandwiches usually have more on them than peanut butter or plain turkey.
If you are worried about putting money into something that might accidentally be thrown away, invest in some of the small Ziploc containers. I promote Ziploc because they have significantly reduced the amounts of plastics used in their products and are BPA free. They are relatively inexpensive and there are usually coupons for them in the Sunday paper. I have read other sites that suggest reusing baby food jars, but I don't personally recommend that because I know how the girls' lunchboxes get thrown around and I would hate for there to be broken glass in there when they open it up. Another plus to reusable containers is that you can make your own Jellos or puddings from the box and then put them in the small containers to chill. Ta Da! Instant single serve puddings and jellos that are ready to pop into their lunches with no waste and tons of savings!