Purchase your hamster's new cage, wheel, water bottle, food dish, chewsticks, bedding, and food BEFORE making the trip back to get your hamster. This will ensure that once your hamster has transferred to his new cage (very stressful for him) that he will have all he needs from the beginning, and that no more changes occur for him the rest of the night. I learned the hard way with my first hamster... I had his cage prepared ahead of time, but did not think to take it with me. Instead, I allowed the PS employee to chase him down, scoop him out, and lock him in a small, dark take-home box. (very professional, right?) He "pooed" all in it and scratched and squealed all the way home, out of sheer fear and stress! He had a very traumatic first night home... Please don't let this happen to your new baby!
Instead, ensure a smoother transfer for your hamster by picking up everything he needs during the day, while waiting until night time to go back and get your hamster. (You may want to find out your store's/breeder's closing time beforehand, and go back about an hour before they close.) The later, the better since hamsters are nocturnal.
Before returning in the evening, assemble the cage, line it with bedding, and add something to gnaw on. Prepare the food dish, but leave it and the water bottle at home for the trip, so that the cage is not soiled during the ride home.
When you return to the PS that evening, take the cage and a mug or small container with you. After selecting your hamster, insist that the clerk allow YOU to let the hamster peacefully crawl into your container. Do NOT allow them to chase or frighten your hamster. If this happens, threaten to take your business elsewhere, (or ask to speak to a manager) and stick to your guns. (Most petstores need major training in the area of how to handle hamsters.)
After your hamster crawls into your container, immediately cover it with your hand, then hold the container up to the open door of the new cage. (cage should be placed on the ground with the door open ahead of time.) Hamsters are naturally curious- he should crawl right in. Promptly close the door of the cage.
After paying, take your hamster straight home- no stops on the way. At home, fill and test your hamster's water bottle. Open the cage door for the last time this night to give him his food and water. Then, leave him alone for the next 24 hours. (Hand-Training should begin the next night, or after 48 hours if your hamster seems aggressive toward you.) The first night is always the hardest. Although he had a smooth ride home, he still may squeal, hiss, or even tear things up in his cage. This is normal and usually only happens the first night, or two at the most. You will be tempted to go "comfort" him- DON'T. He needs this time to adjust to his new home.
The bad news: Hammy is spending his first night away from the only life he ever knew with his siblings- and is grieving. The good news: hamsters have very short memories- and once he gets his new house in order, he will forget about them quickly and move on.