Every day I wear a fanny pack (don't carry a purse) just to the left of center, in front of my body. Since I am so used to it, I use it for trips too and since it is in front, I can casually rest my hand on it and there is minimal concern about pickpockets.
For trips it has about the same things as on a normal day: my wallet with driver's license (photo ID), the credit card I will use on the trip, a little cash, lipstick, chewing gum, bandaids, aspirin, post-it-note pad, pen, photo album including pictures of my kids and past cruises, cell phone, etc, and especially for the cruise, I put our passports in the back pocket. Someone would have to cut it off me to get at any of that stuff. I wear it tightly cinched.
In my backpack I put any item I might want to have before my luggage is delivered. This is my carry-on if we are flying so I have something to read, a water bottle, jewelry I do not want to lose, sunscreen, snacks, etc.
Some people put a change of clothes and swim suit in there so they are prepared for a dip before Life Boat drill and dinner in case a suitcase is lost. I figure I can go to dinner in my traveling clothes since I wear coulottes and a collared shirt.
The backpack works well for day trips (excursions) when in port. We put our glasses cases, sun screen, extra t-shirts since we snorkle in a DARK t-shirt to screen for sun, etc. I am used to wearing a backpack so it is very normal for me.
Jan (53 years old)
