if you have rails, they are more efficient than roads. And it isn't TOO hard to convert a self-propelled vehicle to run on rails.
In terms of "buried" treasure, I suggest the following
1. Chemical Fertiliser.
2. Coal.
3. Some well-wrapped Amazon "Return Pallets". (mostly junk, of course, but some interesting tools and luxuries could be included. Maybe the players can think of a use for a roomba, or a pressure cooker, or a toy drone?)
4. Wind Turbine blades and a transformer
5. Paper. The essential component for (re)building a civilisation. If this is wrapped in plastic it should survive being buried.