I have noticed when doing NH in my 4 cities that some neighbors result in both Gold and Supply rewards but most are just gold. What triggers the ability to get supplies as well? IS it related to my Culture numbers or just luck or based on regular interaction with someone's town? I'm at level 3
Supplies, in addition to coins, are given when you help that neighbor within 24 hours of them helping you. This is indicated by the neighborly help button in menus being golden-colored instead of green-colored. Check your notifications for an easier time getting to those people.
If you're on mobile, though, you're about out of luck with respect to indicators. The notifications only shows in gold if you're both able to help them
and get both coins and supplies. Otherwise you'll just have to trawl through the world map and hope for the best.
Fellowship doesn't count; it's always Easy Street there
That 24 hour window extends further for members in your own fellowship by 4 hours for each level in Advanced Help perk. EDIT2: That applies to all people who visit your city. Apologies for the misinformation.
EDIT: So I guess it is in a sense "luck" which can be somewhat helped if you regularly interact with your neighbor. But yeah, the actual trigger is returning the neighborly help in a timely fashion