How to lock a bag with only one zipper?

Sew a metal ring, key ring, etc., to the bag in the area where the zipper ends.

Put a diaper pin through from the inside. It will give you a sturdy metal piece to lock the zipper to. You can also borrow the diaper pin for emergency repairs on other luggage if you need it.

They still sell diaper pins??
I wouldn't worry about locking your bag. Just be aware of your surroundings when you are in crowded conditions, such as on a train or bus. I've traveled all over using just a regular purse with a single zipper without a problem.

I never pack my digital camera into my luggage. Wear it around your neck and tuck it into your shirt if you want to keep it out of sight. Cameras are so small you can wear it comfortably.

I always wear mine and have traveled that way for 15 years. If you are alert, no one can steal it from you.

I usually have my Civita bag so of course can lock it...but I often don't. Just having a small padlock on it probably discourages pickpockets--in fact I have never had a problem.

Wear it so the zipper is against your body rather than facing away from it.

If the zipper has a hole then the idea of using a safety pin is good. It will deter pickpockets who won't bother trying to undo it. It takes too long.

I put one of those caribiner(sp?) hooks through the zipper pull hole then around the strap. This may or may not be an option depending on the location of the strap, but it works for me! Its not quite a lock, but they have to fiddle with it for a moment to get it open, and youd take notice of that!

Diaper pin....do they allow thjose on planes? Just be prepared for sme questions at security ("so, where's the baby, Osama?").

If it's important to be able to secure that (and it would be to me), I'd take it someplace and have a D-ring or some other attachment point sewn on it. I'm all thumbs and can't accomplish much with a needle and thread, so when I need stuff like this I'll go to a local taylor shop. I've had things like O-rings or additional hand straps added to packs before and it has worked out well.

If the zipper pull has any type of hole in it, you should be able to fashion some type of security to it.

Even a twist tie would work, something to make it harder for pickpockets.

All that being said, if you just really watch your surroundings, stay away from crowds and watch yourself on buses and metro cars/train - you might be OK.

I alway keep one hand on my bag - even when the zippers are locked (I use PacSafe bags), that gives me peace of mind.

The other thing you might consider, is taking that bag back and finding one that has two zipper pulls, or has locking zippers. Unless you are totally in love with this bag, it sounds like it's not ideal for travel.

I don't lock my zippers but I always carry one or two diaper pins and a few random size safety pins for repairs. You can still get them although they might be harder to find than in the past. I confess I made my wife use regular diapers because I didn't want to generate so much paper waste, we have some left over from those days (along with a supply of cleaning rags). They are surprisingly useful but I do keep the baby bunny or duckie head tucked inside.