The two things to watch out for are 1) the young mother nursing her baby.
She is the distraction while someone else bumps into you. 2) is any
pack of young kids. You'll think they are merely begging with their
hands out but in fact they are extremely professional in their pick
Swatting them away WILL NOT HELP. The simple fact is,
they're faster than you are. The two suggestions I can make are 1) keep
a cheap wallet stuffed with paper in your back hip pocket. Keep your
real valuables in a wallet that you wear INSIDE your pants. Also make
sure you make xeroxes of your passports and plane tickets and keep them
someplace other than your valuables or luggage.
You'll also find in catalogs like Travelsmith, you can
buy small, medium or large size day packs with a thin steel cable that
runs thru the strap. That way if someone tries to slice through your
carry strap (a very common practice) they won't succeed. This would be
a good solution to your camera dilemma. Also remember to always keep the
strap over you head, not just on your shoulder.
I know this sounds like a pain, but it's just common
sense. If you use your head, you'll avoid a ruined vacation.