True...
But but is it actually crossing the ocean that people dream about, or exploring whats on the other side of the ocean?
My boat cant cross an ocean, but it is comfortable cruising a coast. For us, and others with a coastal cruiser shipping might be a viable option.
To each his own. To me it's about arriving at the other side, an experience which is intrinsically linked to the time spent at sea. Having something you've never seen before rise out of the horizon after getting beat up for two weeks is absolutely magical. The time at sea does have its own value, as well; I find an inner calm that is unattainable anywhere else, but I know that doesn't count for all.
If it's all about exploring the far coast, the most rational answer is to fly across, then rent a well appointed RIB and stay in hotels when you don't want to sleep on the beach.
But back to the subject at hand:
The bare minimum for a passage maker is something that will absolutely certainly get you there for sure. Anything more than that is pure luxury, and secondary to the first requirement. If you encounter proper nasty weather (which you will if you keep crossing oceans), the coziest thing in the world is a boat you can trust. You're not going to care much for hot showers and fresh vegetables if you rightfully fear for your life.
A lot is being said about reliability of the propulsion system. While that is certainly a very important aspect, even a critical one, I'd be even more concerned with the boat's ability to take a proper beating.
You want small winows, all externally framed. Think 12mm hardened glass and no bigger than letter size, smaller if at deck level.
Exterior doors and deck hatches should all be as strong as the superstructure itself (think steel hatches or equivalent) with multiple locking dogs.
Engine room vents should be of solid steel construction, and placed as high as possible (top of superstructure).
Shell plating and frame spacing should be such as to maintain structural integrity under extreme stress. Look into the forepeak of a North Atlantic fishing boat, and you get the idea.
All masts and exterior fittings should be oversized and built through to the internal framing.
The dinghy, life raft and anything else that absolutely has to be stowed so as to not get hit by green water on the deck, ideally on top of the superstructure, behind the bridge.
The bow should be shaped so as to prevent excessive over-spray: 10-15% of LOA (depending on ship size), and equipped with a wave plow or equivalent
Etc etc, you get the idea. Another point which has gotten surprisingly little attention in this thread is stability. You absolutely cannot over-estimate the importance of a nice stability curve. I've had this happen to me:
...and yeah, that made me appreciate what an absolute horror it is to hold on through the night, half expecting to capsize at any moment.
While OP's question was about the bare minimum and not "which boat would you ideally choose for passage making", I alluded to re-purposed professional boats above, because they tick all the right boxes. Recreational boats, while undeniably much more comfortable, tend to be let down by large window surfaces and the like.
You dudes should have been good like me. 
