3) What do you buy when you get there (before the disaster)?

A local person.

I don't mean anything illegal, like bribing, buying a politician, etc. I'm talking about where you create a legal business relationship between you and someone else. That someone else has your best interests in mind. If things work out, you won't be alone in the middle of a collapse infrastructure.

Downsides:
- You didn't pay enough to keep the bad guys away from you (if you're concerned about this, perhaps you should consider a professional bodyguard)
- They may not help you at all.
- They are killed/incapacitated/unavailable when a disaster hits.

Upsides:
- If you travel frequently to the location, you have someone to receive your packages with your supplies.
- You may have access to an extensive local network of people to help you, or to move you from one place to another.
- Local intelligence (what neighborhoods to avoid, what scams there are, where you can get cheap supplies, what kind of "strange" laws are in the country ("but Mr. Mexican Police Officer, I just had a single minature replica bullet!"),
- They might know where the U.S. Consulate is. (Probably should register yourself at the closest one anyway).