Buy your electrical adapters AND converters at home before you leave. Overseas destinations will most likely have a different electrical current that is not compatible with most U. S. electronics (though many people report their laptops work fine in Europe) that you may carry. Things like camera and battery chargers, iPod chargers, GPS units, electric toothbrushes even. And remember that an adapter is NOT a converter, unless you buy a two in one device.
Always copy your important documents (like vaccination papers, passports, airline and hotel and tour reservation confirmations, Visas, etc) and carry them separately from the actual documents. Getting an emergency Visa is incredibly easier if you have copies of every original.
Make sure you check what vaccinations may be required for the destinations you are heading to. Some shots need to be taken in a series and waiting until 2 weeks before leaving may mean you cannot take off or at the least visit one of the destinations requiring certain shots. Start researching 3-6 months ahead of travel dates.
Take cash, travellers checks, and at least two credit or debit cards with you. In certain locations, debit cards may not be accepted and if you lose travellers check or a credit card, you will have back up funds available to get you through the crisis.
If you carry medications overseas, it is advised by many that you also take your prescription info with you (copies) including if generics are being used. This will avoid confusion at customs. Also, keep meds in original containers with the Doctor. info. on it so as to not arouse suspicion of pills in an unmarked plastic container.
Most importantly, learn about your destination country’s regulations and requirements before leaving. It is up to you to know the laws for driving, currency regulations and health requirements. Also to observe local laws and customs, though knowing all of the current law registry is not expected. But some countries have vastly different laws and customs from the U.S. and ignorance of them is not a viable excuse.
Strongly consider travel insurance. If your home coverage is spotty, can save you mountains of headaches (not to forget debts) if you look into appropriate insurance coverage. And not just medical, but flight cancellations or delays, missed connections, extra hotel stays, lost luggage, thefts, etc.