The power of powernapping is also not to be underestimated. 30 mins of sleep - or even 10-15 - is amazing sometimes. I also deliberately try and avoid long, boring straight roads where possible - Autobahn excepted as the adrenaline is pretty cool. But even 200km/h gets boring after a while, which is why I'll hit the cruise at around 150. Reasonable economy, but I have no "I must be there by x" - I get there when I get there and if I miss the ferry, that's my problem. Same thing with trains - there's another one, later. The hotel know I will be late and have asked me to keep them informed.
I have the return trip - it's either leave at 00:10 to get there "on time" or leave the day before and sleep in a hotel with an opportunity to discover another city. I know which one I'd rather do.. and I have tried driving through the night before, but when you sleep badly and not on the previous boat, it's not fun. If you have passengers, things are slightly different.
Satnav is a great invention, but have a good idea where you're going anyway - for my Gdynia trip, I know it's the E28 out of town, down to Stettin, then it's Berlin and Dresden. I'll check the numbers, because I don't trust navs completely and they do sometimes get stuck. You might also find something you want to check out! So write it down and have it on the passenger seat.
Don't take chocolate to scoff in the car, make sure your phone is charged and if you have a drink with you, open it first.
I realise actually now just how much I take for granted the ability to do these long slogs.... and I do them on my own.
Bret