Most people have some material which they naturally generate as a waste product. For me, that is my bad habit I never set aside time to cure: Soda. I most often buy the 12 pack fridge cases, occasionally the 24 pack cases. For some of you it may be cereal boxes, or maybe a common small size cardboard box from Amazon.
Identify one or more materials that you just always generate. Ideally something which is too small to be very useful as a test cut for future custom designs. Then, plan to use the material in as optimized of a manner as possible (least material tossed in the recycle bin/trash).
What you use the material for should be something consumable (not edible… but something that cannot be re-used hundreds of times), or something nifty enough to give away to random people and put a smile on their faces. Because this is a material you will be generating at least once a month.
You could go the other direction, and plan something massive (like the cardboard full sized car) which will be made using your common generated trash of choice. But aiming for the one-off should result in files which can be shared with other GF users. Little give-away items are absolutely my preference, since you can carry a few with you and hand them to random strangers.