LOL I read the first sentence and was like-omg hay cubes-get those and repackge! lol
I’d take hay and put in brown paper bags with some treats in them. Mine just love them, and how simple! You could also pick up pine, spruce and balsa and sissel rope from hardware store and craft store, and perhaps some natural paper. Then make lovely dangly rabbit toys!
Ensure anything you do is something you’ve purchased before, or check with a vet to ensure it’s safe. List all ingredients on the label, even if something is safe doesn’t mean all pets will react to it the same and the owner should have some info to go to the vet with just in case! (think bakesale-list all ingredients). If you are going to make cookies use all stainless steel so there is no chance of cross contamination (again…just for the purchaser’s sake!)
Another thing you could do is get a bunch of faux sheepskin from the fabric store and cut and sew cute blankets (all you’d have to do is edge the edges) -or stuff them with stuffing and make beds!
Hmmmm and lastly perhaps get grass seeds, and planters and sell ‘grow your own bunny grass’ kits? Cute pots and seeds with some dirt-dirt is dirt cheap you could buy big bag and make lots of kits, and if you got cheap cute pots you could probably get 5-10x what you invest to put them together.