As soon as you get home:  put 1 teaspoon of Karo syrup or honey into your new pup’s mouth. The pup will not have eaten for as many as 10 hours and will need sugar to avoid HYPOGLYCEMIA. Offer water and put the pup into "dog jail" to go potty, stretch the legs and relax. Pup must be allowed time to potty to avoid urinary tract infections. THIS IS NOT THE TIME TO HANDLE THE PUP!  The pup will likely be eager to eat. I like to give them dog food that has been softened in hot water. The pup will be used to this and I generally feed them soft food until they are about 10 weeks old. Softened food is easy to consume so they usually eat until full and they become hydrated at the same time.  You can have the food ready in frig before hand to feed when the pup comes home.  Measure out a few tablespoons of food into a dish. When that is gone, put more out and so on.  You want to know HOW much food is being eaten. Don't be alarmed if the pup doesn't eat right away, but the pup must drink water so be aware of that.
Pups generally let you "know" when they want only hard kibble.  When they are no longer eager for soft food, I put down some hard and usually it is gobbled up. This is how you know to make the switch permanent.

Pups here are housed together in a heated puppy room, about 78', and they usually curl up together.  Warmth is essential and you should not consider the temperature that you may be comfortable at, to be adequate for your pup living on a cold floor.  I recommend a heat light over pups or a heating pad for pups to lie on. You can get a trouble light ($7) and red heat bulb ($10) at most hardware stores. The light will clamp onto dog jail and provide warmth for the pup. Here, I use heating pads all the time. The Sunbeam brand ($12) usually set to low is ideal.  I slide the pad into a pillowcase and safety pin it closed.  Use the silver duck tape to secure the cord onto the floor. Be sure to read the information provided with the box. Many heating pads have an "automatic shut off".  You need one that will stay on 24/7.  Be sure the pup has enough room to get away from any heat source that you use.

To keep STRESS at a minimum don't over-handle your pup.  During the first few days, the pup should be left alone to get used to the smells and sounds of its new home. I encourage reaching in and patting the pup, while letting the pup lick your fingers etc.  When you take pup out for much needed exercise, play with it on the ground. Don't hold and cuddle it, but rather let pup have the freedom to run up to you and climb on you.  When a pup is in control of this fun activity, it will begin to build confidence and will feel secure in its new home.
I don't consider it a problem if the pup doesn't eat for a day due to the stress of the relocation.  HOWEVER, I want you to put Karo or honey into you pup every few hours to keep sugar levels up. I don't want pup to be lethargic. This is a sure sign of stress and possible hypoglycemia.  As long as pup is drinking and going potty it likely will eat by the next day.