@MissMuffet - Sorry, but I'm going to give you some bad news. There used to be some opportunities in this field, but these days airline security requirements have changed everything.
Not that it was ever super easy in the past of course. Becoming a courier of international deliveries required you to be free at short notice, look smart, and be able to travel with only a carry on bag. (Remember you may be then left to amuse yourself for a few days or a week, with limited clothes!)
The idea was that your luggage allowance was taken by the items you were technically escoring to the destination. This often wasn't a very glamorous location, not all courier packages are sent to Paris or New York!
My company used to employ international couriers, but these days someone from the office gets this duty. It's a pity as this takes us away from base, and our busy workloads. I hope one day in the future these jobs will be opened up to travellers again.