As a general rule, most countries require passports to be valid for at least 6 months from the date of entry.
How to Obtain a U.S. Passport - U.S. Passport service guide
Find a passport office near you - U.S. Passport office information
U.S. Passport expediting services - How to get passports fast.
Depending on your country of residence some countries require foreign visitors to obtain visas in advance. Other countries will issue a tourist visa upon arrival at the port of entry. It will depend on your citizenship and what countries you are visiting. The following website is a good reference - VisaHQ.
For U.S. citizens, visas/tourist cards are required in order to enter Paraguay and Suriname.
Paraguay – A Tourist Visa is required for citizens of United States of America to enter Paraguay. A visa can be applied for online or directly at a Consulate of Paraguay. U.S. citizens can also obtain a visa on arrival* in Paraguay for a stay of up to 90 days.
*This is ONLY available at Silvio Pettirossi International Airport in Asunción (ASU) and the fee of US$160.00 (as of June, 2018) must be paid IN CASH. Entry via any other airport or land border crossing requires a visa in advance. Passport must be valid for at least six months from the date of your proposed entry into Paraguay. Passport MUST contain one blank visa page for the visa to be issued.
Suriname – E-Tourist Visa (multi-entry) or E-Tourist Card (single entry) is required to enter Suriname. Visa or Card can be obtained online here.
All persons entering Suriname must have their yellow fever vaccination and their international yellow fever card.
Brazil - As of June 16, 2019, U.S. citizens do not need a visa if they are traveling to Brazil for tourism, business, transit, artistic or sport activities, with no intention of establishing residence.
Bolivia - Bolivia tourist visa is not required for citizens of United States of America for a stay up to 90 days.
**Yellow fever vaccination is recommended to people travelling to risk areas in Bolivia, such as:
Some hotels will let you use their facilities (gym, spa, pool, beach, etc.) for a reduced day pass. This can be great for layovers!