Start to compile some hardy items, like toilet paper or paper towel rolls, small boxes, construction paper, newspaper, milk jugs, egg crates, plastic containers, tubs, as well as plastic utensils and things of similar nature. It is better to have more than less; so, do not hesitate to save more items than you think are necessary.
Consult recycled craft websites (for example, Kids Craft Free Projects and Free Kids Crafts) to search by either the craft that you want to make or by what material you have. Kids may find it more fun to see what they can make and work backward, whereas adults or teachers like to plan ahead by looking up what materials they will need and work forward.
Know which craft you want to make. One example that Kids Craft Free Projects has listed is clothespin holiday ornaments. For this project, all you need are clothespins, fabric scraps, washable paint and glue. You will find many craft projects on both sites, and they are all simple and fun to make.
Keep track of which items you are using, what you need to accumulate more of, and what sits idle as other crafts are being made. There are definitely more options than listed on either site, or any website, for that matter; so, check out other resources (like the library) as well as brainstorming sessions with students and other teachers or parents.