Current solution to manage monetary expenses among friends already exists. Apps like splitwise, GroupMe or Square Cash already provide a very useful tool when doing trips, fairly allocating debts and keeping track on who owns that to whom and how much.
In a personal experience, I used Splitwise with 7 friends for a trip to Menton in France. We rented a car from munich, and from the beginning we agreed that instead of collecting money after each joint expense, one (the person who owns the most) will just pay for all and put it in the app. At first I was skeptical since I was more used to do Excel sheets and collect the required data there... Quite old school.
After the trip, I was amazed by the amount of money we spent, and how at the end of the journey all the settlements were basically lower than 2 euros!
We never have to deal with splitting bills on the table or using calculators while the waiter waits.
Nevertheless, after a couple of months I realized, that one particular person how I though owned me money (like 10 euros) apparently let me 4 euros for a beer which I don't remember drinking. I talk to other peoples, and at the end we kind of have a discussion since some of us were thinking that people were just randomly adding expenses without others notifications with the purpose of settling the balance. I don't blame them since they were thinking that the others where doing the same.
That's the reason why I wonder, why isnt there an app supported on block chain so any expense registered on the network requires approval by the members, and cant be altered after registered?