Minimum vaccum line is the one that connects the distributor to the carb. Whether manifold vacuum or ported is oft debated but if it ain't connected the vacuum advance is not going to do anything for you.
Second most important is the manifold vacuum to brake servo. This can be eliminated by taking the servo off but generally it works better with one.
After that there is all sorts of stuff you can hook up. I make do with just the above, my EGR valves are all non operable, the tank is vented through the gas cap, the TAC was lost years ago etc.
Don't forget the PCV system that sucks out harm full crankcase vapor. Unless you want to run a road draft tube but the crankcase needs to be vented.