I don’t know why there is a big difference in some paper and toilet paper rolls, but I have found some have these little glue areas and for the most part they are thin or almost non-existent, while others seem to have heavier/thicker dried glue lines. Those I avoid, but otherwise toilet paper rolls and papertowel rolls are a great toy. At SaveABunny, they put a hay in the rolls and called them hay bombs. It was a great economical way to offer the bunnies some chew toys.
Cardboard is generally safe as it digests just fine, but like Jersey said you do have to watch for what was stored in the box (as some boxes are lightly sprayed with pesticides if they carry certain foods and of course waxes, and paper/boxes that have lots of print, you’d have to watch for.
For more info on cardboard/paper safety, I found this from one of Dana Krempels (allexperts.com) answers:
“As long as the paper and cardboard have no print containing heavy metals (as many colored inks do), there is no harm in your bunny eating it. Paper is made of cellulose, which is digestible to rabbits.”
FULL RESPONSE: http://en.allexperts.com/q/Rabbits-703/eating-paper-2.htm
.Now obviously, if you bunny fills up on paper in place of a healthy diet, then that would be a problem and you’d have to cut back on his cardboard toys.