Shinkansen, traveling unreserved?

I actually always traveled reserved on my last trip with a JR pass. The one time I wanted to travel unreserved, standing up (as the train was fully booked) the ticket attendant told me that this was probably not possible on a pass - he didn't sound too sure about it, and it didn't really make sense.

Does unreserved mean that I simply show my pass to get into the shinkansen area, board and show it when tickets are checked, then show it again at the other end to exit?

You say the train was "fully booked", was it an all-reserved one ?

The one time I wanted to travel unreserved, standing up (as the train was fully booked) the ticket attendant told me that this was probably not possible on a pass

My guess is that the train did not carry unreserved cars. If a train does not have unreserved cars, then you cannot just ride the train. You have to make seat reservations. And if the train is booked out, then you have to make an advance reservation for a standing ticket. The Hayabusa, Hayate and Komachi trains on the Tohoku/Akita/Hokkaido Shinkansen work like that.

Does unreserved mean that I simply show my pass to get into the shinkansen area, board and show it when tickets are checked, then show it again at the other end to exit?

Yes, but again, you cannot ride a shinkansen that does not have unreserved seating. Also, if you do not find a seat in the unreserved car, then you should stand in the unreserved car. Unless it is extremely crowded with other standing passengers, you should avoid standing in a reserved car. And it is not allowed to stand in the Green Car.

And, of course, you cannot ride the Nozomi and Mizuho with the Japan Rail Pass!

There are reserved cars and unreserved cars. You cannot sit/stand in reserved cars unless you have reservation. Some trains have no unreserved cars. On Tokaido Shinkansen Line, Japan Rail Pass cannot be used for "NOZOMI" train that is fastest while HIKARI/KODAMA stops at more stations and slower than NOZOMI.

Doe this info help a bit ?

It definitely had unreserved sections as it was a Hikari leaving Osaka for Tokyo.

The Hayabusa, Hayate and Komachi trains on the Tohoku/Akita/Hokkaido Shinkansen work like that.

And the Kagayaki on the Hokuriku Shinkansen, too.

In any case, the JR Pass website does not mention standing travel at all, so this question cannot be answered without looking at the complete rules, which as far as I know are not available online. (Maybe try asking a JR company if you are interested.)

It definitely had unreserved sections as it was a Hikari leaving Osaka for Tokyo.

And you were standing in the unreserved car?

My guess is still that it was some kind of misunderstanding on the conductor's and/or your part.

If you stand in the unreserved car of a Hikari with a valid Japan Rail Pass, you do not need any additional ticket.

That's interesting, I have booked Tokyo-Shin-Aomori online, and can't book to Shin-Hakodate - but google maps tells me that the same train goes all the way. Could I in theory just stand up for this section if I'm unable to get a ticket? I'm told that you can only book Aomori-Hakodate (and the limited express to Sapporo) once you're in Japan. But I don't think there will be any seats left as I leave april 30 and come back to Tokyo May 3!

Were you using the JR East website? Could it be that the Shin-Aomori to Hakodate section belongs to JR Hokkaido and you cannot reserve it on the JR East website?

John B Digs Japan, I've taken a look at the JR Hokkaido site and can't find anywhere online to reserve anything. There's just no option for it unlike the JR east site.

Well, some JR companies may not allow you to reserve online or online in English. I haven't had a need to reserve that far ahead when I'm outside Japan and I've never had any problems getting my reservations.

If you don't get your first choice, reserve the first train from Shin-Aomori and spend the night in Aomori if needed.

I take it Aomori isn't a bit enough city to have capsule hotels? I'm only paying Y2700 a night for one in Sapporo.

I paid 4100 yen for Toyoko Inn Aomori Eki.

Go to a JR ticket window and book?

Hakata14, just worried about them running out on april 30 and may 3, due to golden week.

How many trains are running those days?

Looks like about 10 a day between Shin-Hakodate and Sapporo. At least, 10 that would connect with the shinkansen at Hakodate.

Golden Week is short this year: two three day holidays instead of 6 days. That means people may not travel much, especially that far north as most would fly to save time. I think you'll be alright.

Cheaper and quicker to fly. The Hokkaido Shinkansen isn't a huge success. I'm doubtful you'll have issue getting a seat.

I have booked Tokyo-Shin-Aomori online, and can't book to Shin-Hakodate

English online booking is not available for the entire distance.

Could I in theory just stand up for this section if I'm unable to get a ticket?

No. You need a seat reservation or standing ticket in order to ride the train. Standing tickets are only available when all seats are booked out. But I think it is rather unlikely that the section between Shin-Aomori and Hakodate is going to be booked out. They are very large trains, and the Aomori-Hakodate section tends to be a less popular section. Most people get off at Sendai, Morioka and Shin-Aomori. Of course, new people are boarding, as well, but their number is usually smaller.

But I don't think there will be any seats left as I leave april 30 and come back to Tokyo May 3!

I disagree as explained above. But I cannot guarantee 100%.

And here is JR Hokkaido's reservation site, but it is useless because tickets have to be picked up in Hokkaido:
https://www3.jrhokkaido.co.jp/rail-en/html/step03.aspx