I am going to say, 'Don't use junk wood! If you 'practice' and it turns out nice,
have it turn out nice on a good piece of wood.'
To me, "There is no practice wood."
That said, boxes and pallets are still a good source of wood.
Just clean it up, make it look nice so that when you finish
cutting a scroll piece on the wood, it will be nice enough that
you would give it to your spouse.