First of all, as a short term measure, can you move the freezer to a more accessible location?

For the long term, consider that getting rid of it all at once without the agony of selling one by one, dealing with prospective buyers, all for little gain is the way to go. Donate what you can to a thrift shop and take the tax deduction instead. The lifting of this burden will be immeasurable once it's done.

Much of the construction leftovers will really be of no use to anyone. It is illegal for a licensed contractor to install old toilets if they are not of the low-flush variety. Our local Habitat for Humanity will not take appliances that are more than a couple years old. You may find someone who will come and collect metals to sell for scrap. Or you can take it to a scrap metal dealer yourself.

If he can build a rack to store GOOD useable lumber, plywood, great. If it's stored neatly you'll be able to get to and use the pieces you need. If you have to spend a lot of time removing nails, screws, it may not be worth it to save.