Cancun Honeymoon,....Need Tips for How to Behave In Foreign Country...

You've had two suggestions about Pam keeping her purse on her shoulder. I'm going to go a little further and say have her take a purse with a long strap so she can wear her purse on her opposite shoulder (purse strap over left shoulder but purse under her right arm type of thing). That will make it even harder for a "grab and run".
Also, be careful and extremely respectful. I had a US employee almost thrown in a Mexican jail for sitting on the base of a flagpole in front of a Federales police station while waiting for a ride. The Federales got all bent out of shape claiming he was "disrespecting" the Mexican flag flying on the pole.
Above all, remember you're not at home. You'll be playing under another country's rules.
Have fun, be safe, and leave whatever you get in Mexico there!