Gringo Trail

Tips for travel in developing countries and Tropical diseases apply in most countries on this itinerary, with all diseases of the "big mosquito trio" (malaria, yellow fever and dengue) being present in many places.
Latin American countries in general have a more relaxed visa policy, with many more nationalities being able to enter the countries visa-free than the Schengen Area (not to speak of the United States). Westerners are in general able to travel visa-free to all Latin American countries, though there may be all sorts of entry and exit fees when crossing borders (ranging from a few USD up to 20). Argentina, Brazil and Chile, however, have a policy of charging citizens of certain large English-speaking countries as much for a visa as their citizens are required to pay when they wish to travel to the USA, Canada or Australia. There is (in theory at least) a common travel area encompassing Honduras, El Salvador, Guatemala and Nicaragua called CA4, but the effect this will have on you is probably minimal as most people get visa-free entry to those countries anyway. You may benefit from no entry fee being levied traveling between those countries, though that is hit or miss. If you are charged a fee at one of the borders of one of those four countries to another of those four, being polite but firm may go a long way in convincing the border agent otherwise.
Outside tourist destinations (and not necessarily even there), English is not widely spoken. Study some Spanish, or if you head to Brazil, Portuguese before your trip. Beware that the pronunciation and grammar differ from the versions spoken in Europe. Some terms may have a different slang meaning and some slang terms may not be commonly understood. While you should have no big problem speaking European Spanish, pitfalls like "coger" (meaning "take" in Spain but a vulgar term referring to intercourse in much of Latin America) may on occasion draw laughter from locals. In the Andes a smattering of Quechua or Aymara doesn't hurt, but if you're on the tourist trail, Spanish or Portuguese is all you really need.

These are some of the points considered to be on the Gringo trail. Unless you're driving yourself or flying, you will probably be traveling by bus.
Be aware that it's practically impossible to pass overland between Panama and Colombia; the Darien Gap stands in the way. It is however possible to arrange a crossing on a ship.
Be aware that travel connections are not as good as they are in the US or Europe. For instance Tegucigalpa - Managua is only 300 km as the crow flies, but only one airline offers direct flights and the bus takes six hours. Due to less competition, airfares can also be quite high.

Mexico

Cancún, Chichen Itza, Isla Mujeres, Tulum, Guanajuato, Querétaro, Puerto Escondido, San Cristóbal de las Casas, Oaxaca

Central America

• Belize: Caye Caulker, San Ignacio (Belize)
• Guatemala: Antigua Guatemala, Lake Atitlan, Tikal, Semuc Champey

• Honduras: Bay Islands, Copan
• Nicaragua: Granada, Leon, San Juan del Sur, Ometepe, Big Corn Island and Little Corn Island
• Costa Rica: Montezuma, Puerto Viejo de Talamanca, Jacó, La Fortuna and Arenal, Nosara, Manuel Antonio National Park
• Panama: Bocas Del Toro, San Blas Islands, Panama City (especially the Casco Viejo), Lost and Found Jungle Hostel (Las Minas, Chiriqui)

South America

• Colombia: Cartagena, Taganga, Tayrona National Park, San Gil, Medellín, Bogotá, Bucaramanga
• Ecuador: Galapagos Islands, Montañita, Cuenca, Quito, Mompiche
• Peru: Cusco/Machu Picchu/Inca Highlands, Lima, Trujillo, Arequipa, Puno
• Bolivia: Salar de Uyuni, Potosí, La Paz, Copacabana
• Brazil: Fortaleza, Olinda, Salvador, Rio de Janeiro
• Uruguay: Colonia
• Argentina: Iguaçu Falls, Buenos Aires, Mendoza, Ushuaia
• Chile: Easter Island, Pucon, Torres del Paine, San Pedro de Atacama

Perhaps even more than in other developing countries, bring American dollars as they are quite widely accepted. Ecuador, El Salvador and Panama actually have adopted them as their official currency, and in some countries prices on more expensive purchases may even be quoted in USD, rather than the less stable local currency. Keep in mind that many Latin American countries also use the "$" sign for their own currencies. While even expensive items may be cheaper in local currency than dollars, local currency will often be hard or nigh impossible to exchange beyond the immediate border region. Even Mexican Pesos, Argentinean Pesos and Brazilian Reais may be difficult to exchange or fetch bad exchange rates once you leave those countries. Euros are only accepted in very touristy places and even there only at bad exchange rates. The Euro is the official currency in French Guyana but this region is usually not considered part of the Gringo Trail.

Coca leaves are legal and widely available in Andean regions, and coca tea is frequently drunk by travelers to alleviate symptoms of altitude sickness. However, cocaine is illegal in these countries, and coca is illegal in most other countries, so enjoy it while you’re there, but don’t take coca home.

This corner of the world is infamous for violent street crime and has some of the world's highest murder rates per capita. Some countries, perhaps Colombia in particular, are also associated with drugs — but steer clear! While you might assume that there is a cavalier attitude towards drugs from tales you've been told (or indeed one of the countless Latin American "narco-novelas"), laws are strict and if you happen to be the one that the law is enforced upon you are looking at a lengthy sentence in prisons that are worse than even those of the US. While your status as a "rich foreigner" might give the illusion of protection, in some cases local authorities will make a point of being especially rough on you to show that the law applies to everybody. Unlike much of Europe, there is a zero tolerance policy towards all drugs and with a few exceptions (most notably Uruguay) even a single leaf of hemp can possibly get you into trouble.
In many places there are rules that you should take a guide or even a police escort on certain hikes. Follow those rules. Guides are cheap and can point out local wildlife and police escorts are only mandatory if there's a good reason.
Most of the destinations are also places where earthquakes and volcanic eruptions may occur. Sunburn is also a risk, as is altitude sickness in the Andes.

• Caribbean
• United States
• Antarctica — though certainly not for the average backpacker's budget
• Banana Pancake Trail — the Gringo trail's Asian twin, roughly between India and Indonesia and the Philippines
• If you are on the trail, it is almost always worthwhile to stop for a while and deviate from the "main route" to less touristically known destinations. True less people will speak English, but the crowds are smaller and many of the attractions are no worse than those the Backpackers congregate on.