Bring a pen. Fill out your customs entrance on the plane. Saves you so much time and hassle.
Make a list of what is in each suitcase. Email it to yourself and/or your emergency contact. This will make declarations easier as well as knowing exactly what was in a suitcase if it gets lost. Do this for both outbound and inbound.
Snap a picture of your luggage. Not only will make a cute social media post but it will save you time if it gets lost.
No matter your opinion on credit cards use, currency exchange, or how much cash to carry when you travel, have enough local cash on hand to get you through a day or two.
Ask the flight attendants where they like to eat while in town or one thing you can’t miss. Some of my best tips come from flight attendants.
If you get stuck on a long layover and want to venture out, ask gate and ticketing agents for tips. Our best Honolulu tip came from one. Oh and try to find a place to drop your luggage in the airport. Many have baggage holds or lockers.
Try to adjust your sleep schedule a few days beforehand and on the plane to your new local time zone.
Know the rules before you go. A pocket knife in the US can be illegal in the UK.