I am presenting at a conference in March and plan to get there by train. The ride is short, so there is no checked luggage, and you're only allowed to have two carry-on bags. The poster tube obviously exceeds the maximum allowable height of a carry-on. Have any of you tried to take a poster on board an Amtrak train?
According to official Amtrak policy, carry-on luggage length is limited to 28 inches, or a little over two feet. A standard poster tube will be 42 inches, or three-and-a-half feet long. Obviously this breaks the published length limit. However, from my experience with Amtrak, the train personnel are usually lenient about enforcing this policy, as long as your luggage is not intruding on other passenger's space or posing a safety hazard in some way. If you can get a window seat, you should be able to prop the poster tube in the corner without a problem. Even better, leave the poster in the luggage rack as you enter the train--these racks are designed to hold larger suitcases and duffels, which are tacitly considered to be carry-ons, but are too large to fit in the over-seat bins. Your poster should be fine there.
Disclaimer: I have not tried to travel on Amtrak with a poster tube, but it should be possible to do so without problem.
Depending on the details you want to present on your poster (in terms of optical resolution [dpi]) you may consider printing your poster not on paper, but on cloth like fine cotton or silk. (I do not refer to canvas.) Several times I saw this at conferences in Europe and the U.S., esp. by Japanese colleagues. On travel, it is cheap in terms of storage volume and mass to carry, fitting even in the bag of a notebook.
Depending on your copy shop, you may be limited in the number of colors printable (some use ink jet technology). Yet details as reaction schemes for synthetic organic chemistry are possible. After the print, you may fold it; arrived at the hotel you simply place it next to the shower (the hot vapors will get rid of the wrinkles, alternatively, or use an iron).