A cardboard box for whelping will not do, it will get soggy and will be a pain to deal with. I heard alot of people taking those huge storage bins and using them as a whelping box. You can even cut a hole in it if you want and it is easy to clean. Most of the time the won't go into their whelping box until they are ready to go, and then they still need encouragement, not all of them want to have their puppies in there, you just have to have them stay in there when she starts going into labor.
For whelping supplies, here are a few things to have:
Thermometer, to tell when the time is near
Scissors, make sure they are sterlized first, for cutting umbilical cord
Dental floss, braided umblical tape or hemostat for tying off the cord
Towels, you will need plenty of towels
Bulb syringe, used to aspirate pups once born
Iodine swabs
Alcohol pads
Antiseptic, to apply to umbilical cord to stop bleeding if there is any
Milk replacer and bottle, incase mom can't or won't nurse them, this needs to be a special formula for newborn puppies such as Esbilac, you
can't give them regular cows milk.
Nutri-drops, will help weak puppies
Scale, to measure them each day to make sure they are gaining
Gloves, to assist delivery
Vet's phone number and emergency vet number and phone near by
Heating pad, to lay under box to keep puppies warm
Notepad, to record how many puppies are born and their weights
That is all I can think of right now, but I know I am missing some. Everyone feel free to add on.
Also, here is a good website to refer to, tells you how to cut the umbilical cord, aspirate puppies, etc.
www.debbiejensen.com
I hope this helps. Good luck on the upcoming birth!!!