But what if a friend conveniently "forgets" to reimburse you for travel costs after the fact?
Oliver suggests sending a tactful email and not letting someone off the hook even if they he or she had to bail at the last minute. "Sometimes, starting it with a 'Hi, hope all is well!' helps too," she suggests, continuing, "'Just wanted to let you know that you still owe me $150 for the round-trip train fare. I was sorry you had to cut out early, and I hope to spend time with you again soon. Please mail the check to:' and provide your address."
Having each person cover different aspects of the trip reduces the likelihood that one person will get stuck with a huge credit card bill. "Agree with the group that any outstanding payments will be resolved within a short amount of time, like one week," Pressner says. "In the past, I found it was easier to use PayPal to transfer cash between friends because most people have accounts, and it was worth it to lose the transaction fee to ensure that I would get paid back."