As to travel documents, a photo ID that has been notarized is a public document inside any of the united States. To make it a public document in any other country signatory to the 1961 Geneva convention (abolishing the requirement for legalisation of foreign public documents) an apostille issued by the secretary of state (of the state not the federal govt) costs only $5 per country.
http://www.hcch.net/index_en.php?act...ns.text&cid=41
I made three pedestrian crossings to Mexico earlier this year on my ID. No checkin at all on the Mexico side and Border Patrol talked to me for a minute or so each time coming back. One of them even informed me that U.S. citizens would require passports to return in 2008. I simply nodded and agreed with him that they would.
If I were going to a country not signatory to the 1961 Geneva Convention or to one that had tangled relations with the U.S. I believe I would send my travel documents to their embassy first to see whether a visa or special permission were required first. Seems prudent. As to going to the U.S. embassy for assistance should the need arise, why not. The agreement between the states called the Constitution is still in effect, isn't it? If not then maybe it is time for another revolution.