As others mention, there are many. I also tend to think of conversations with people I wouldn't normally encounter in my non-touring life, e.g.
a. The woman in Tatarstan, Russia who invited us into her home and started sharing scrapbooks and photos. She was originally from Uzbekistan and had migrated with others in her family and could related earlier travels all through the former Soviet Union and eastern Europe. All this started from a simple request to photograph he carrying two pails of water from the well.
b. The man and kids in wilds of Siberia who brought us into his house, shared vegetables from the garden and relayed what life was like.
c. The guy in the Savannah Amtrak station, where we passed a few hours waiting for a train. We were from pretty different walks of life, but shared simple humanity in common.
d. The guy at the youth hostel on Nantucket who felt so moved by my friends account of crashing her bike into a parked car - that he donated his bike for her to continue the trip - despite multiple "are you sure" requests.
e. The folks in Thailand who gave a ride when my hub broke; and then brought me to a "fixer" who worked in vain. Also the guys in the fruit truck in New Zealand driving to Napier to pick up fruit and saw me walking along the road with broken down bike.
f. Conversations with many "Grey Nomads" driving Australia who gave me their perspectives on things Australian including relations with aboriginals, the monarchy, etc.
g. The folks at the lodge on the Alaska Highway who opened earlier for a touring cyclist, but also made me wonder a little about their mental health (enough so that I figured out how to get out of the room by dropping panniers out the window if necessary)
h. The dozen people and one infant who watched me change a tire in South India, when I thought I had stopped in middle of nowhere.
i. The guy at the Ukraine bus stopped who offered us a spot on his floor after a surprisingly long day.
j. The girls at the phone store in western China who found it incredibly funny to see this tall western man try to buy a SIM card for mobile phone - but were helpful nevertheless.

There are lots more, but these types of interactions are particular things I think of as memorable occasions...