For walking in the neighborhood I would carry the following:
A whistle
A can of OC spray (MK3)
A surefire G2 flashlight
A cellular telephone
Driver's license
Medical Insurance Card
A couple of Powerball Gel packs (or similar)
Any emergency medications (glucose tabs, insulin, nitro tabs, etc.)
Small FAK
Water

All of this can be carried in a cammelback (or similar) or in a waist-pack (like these)
http://www.rei.com/online/store/Search?s...ING_HIKING_LD:N

To avoid becoming a victim of a strong-arm robbery or similar, don't look like a victim. Be aware of your surroundings. Look at people as you walk past them. Don't have earbuds on listening to your ipod, etc.