Before you travel, work out your data plan for your telephone. It is very
useful to access the web from your phone, but without making special arrangements, it may be very costly.
Avoid disappointment! Check for holiday closings in the places you visit.
Some information on international airline travel restrictions always change.
Look them up. Remember that the overhead luggage space on domestic flights within Europe is tiny.
Consider the safety advice:
There still are countries where even tourists need a visa. Check the U.S. State Department.