Mine love toys it keep them busy contantly changing over old cerial boxes and egg box s etc for them. They love an old welly too dig into as well.
I change things around so they don't get bored. I have too be careful what I do rig up though as my hob has a death wish so things need too be very safe.
Any boxes that go into the recycling go too the ferrets first apart from any thing like washing powder boxes and that. One goes in the box and digs and the other jumps up and down on top of it funny as hell