Handling the Finances
The last thing you want to do while on vacation is worry about money. Apps like Spendee (free) are great for creating a budget ahead of time, so that you can gauge how many activities and restaurant visits you can afford before you leave.
Once there, we found Splitwise (free) to be really helpful for cost splitting. It had each group member enter items they paid for, from rental car fees to pitchers of margaritas, and then tallied how much each person owed. Splitwise connects to mobile payment services Venmo and PayPal, so you can pay your friends back with a few taps.