If you have ever watched 'To Catch A Smuggler" on one of the streaming services…
Especially Internationally, never carry anything someone else gives or packs for you unless you know specifically what it is. Yeah, I know, you would never be a drug mule, but that cousin of yours who asks you to take a birthday gift for a relative?
There are limits to how much cash you can have on you. If you have valid reasosn to carry large amounts, make sure you can show where it came from.
Know what limits and restrictions the countries have before you bring in food, meat, fruit and so on. Even to Hawaii from the Mainland, there are severe restrictions on fruits and items. SOmeone smuggles green unroasted coffee in his luggage to Hawaii and it was taken from him and he was fined heavily. That is the kind of thing that decimated our coffee crops here where amny farmers lost upwards to 75% of their crop.
International travelers can have all their luggage and cellphones inspected. Those sexy photos you have of your spouse will be seen if they want to look. Also you may be required to open that secure, encrypted folder on your phone and perhaps those ‘dating’ apps are illegal in the country where you are visiting.
If you think you know what is restricted or not, guess again. You cannot send playing cards to Germany via mail. I dunno if that also means carrying them with you. No chewing gum in Singapore and other crazy laws.