A junket is a pleasure trip, often funded by someone else. You've probably heard of a politician taking a junket to a fancy resort, all paid for using taxpayer money.
A junket can be used as a gift to try to get something from the person going on the trip. If you're a travel reporter and resort owners pay for your junket to check out their new property in Hawaii, you might feel like you owe them a good review. A junket isn't always devious: the word can simply mean a journey taken for pleasure, like when you take your boat out and sail down the coast for a couple days.