I agree with the ones before me that essentially said to rule #1 is to leave the puppy at home. IF someone specifically includes the puppy in the invitation, then by all means, bring the crate for if needed, and keep it on a leash (attached to his belt) the entire time. But otherwise, leave the pup at home. If he is not comfortable leaving the puppy at home for the length of time he plans to be gone, then he needs to adjust HIS plans: shorten the length of his visit so he can return home sooner, consider having a pet sitter or leaving the pup at a kennel. If he doesn't like THOSE options, then decline the invitation.
Dogs are WONDERFUL. But they are a responsibility as well. I think it is great your son got a puppy. Now he needs to step up and be mature in his expectations. In my opinion, it is a TERRIBLE time to bring home a new puppy---lots goes on during the holidays and I'm sure your son will be very busy socially. But, he made the choice to get the pup now, so he is going to have to deal with what that means... which may mean he misses out on some things this holiday season. OR, he may have to deal with the fallout for not missing (messes in the crate at home when he returns).
Really, unless he is a partier and plans to be out for 5-6 hours at a stretch in the evenings, then his pup should be fine at home in his crate.
If you want are willing to have your son bring the pup into your home during the holidays, know up front that there WILL be accidents on your floor. And your other guests (if any) may or may not be thrilled with the puppy being there.
Our dog does not go to other people's houses. Period. She is here if we host something, but everyone knows that. We don't "put her up" behind closed doors or in a crate either. She is well behaved and friendly, but is a dog and knows where she belongs and where she doesn't (the table, on the furniture, jumping on people, etc).
Beyond that: if he has his dog with him while out and about.... NEVER assume that a person is "ok" with the dog sniffing them or being too interested in them or their things, or that they want to pet and be friendly with your dog. Some will. Some won't. Some will be interested to meet the pup, but then are DONE and want their hands washed and not to touch the dog anymore. So don't EVER assume.