I stuff toilet rolls with hay - it keeps the hay neater and they get to relocate it to the most appropriate position to eat it from at that particular moment if they deem their litter tray unsuitable.
If you want something that rattles in a toy I would try a treat, or something larger such as bottle caps.
I use a lot of baby toys for my rabbits - I buy them really cheap at garage sales. The latest favourite is a small (fish sized) toy tractor which I have deemed a supervision only toy because of Terry's tendency to eat everything. But he absolutely loves it and pushes and shoves it everywhere. I haven't tried them yet but stacking cups and bowling pins apparently also make fun toys.
I have made a digging box by cutting a hole in the side of a washing basket and filling it with shredded paper. I bury treats in it sometimes for fun. They once managed to get hold of the bags I keep the shredded paper in too - apparently that was the best toy and my study was buried 30-50cm deep in shredded paper!
I have an old cat scratch post I have given the rabbits now, which Terry just discovered gets the sun most of the morning and so naps on it constantly now.
Anything you DON'T want them to have is probably a very fun toy too.
My previous bun, Ogg, loved to drag her polar fleece rug everywhere. There was a certain spot it had to end up each day.
They also seem to love those little cat bed/cave things. Those little foam boxes covered in fabric with a hole in the side. They love digging in them and destroying them, or in Terry's case, sitting on it and crushing it out of shape.
I know lots of rabbits love and are fine to give pet safe soft toys too (no removable eyes, nose, etc). Ogg had a small stuffed bunny she liked. Terry likes toys too. He likes to chew the ears off them, and also the feet off larger ones. Toy bunny ears are the best to chew off! He has removed the ears from Ogg's rabbit, and also found my giant stuffed bunny I got as a kid and had nowhere else to put and got the ears half off that! o_O
I made them a paper plane the other day. I'm not quite sure what happened to it actually. I think it got thrown off my desk and flattened. But different folded paper/origami would probably be lots of fun for some bunnies. I need to try it with my two more!
My local RSPCA stuffs pinecones with treats.
I recently bought a cupcake tray from a garage sale (can you sense a theme here?
) and I stuff it with different treats/food. Now that they know how to get it out I plan to put lids and stuff over it to make it more challenging. I think there are some photos in the June photo thread if you are curious.
I basically use anything rabbit safe that I see lying around. Before I bin it I ask whether the rabbits would like it.
Terry also loves skateboarding.