Well, I ran out last night
Was on my way home on the highway and noticed the flashing bar, pulled off the first exit to get gas (not sure how long the bar was flashing but I was about 15 miles from the start of my trip). I didn't notice the illuminated warning lamp.
I passed up the first gas station because they are known to have bad fuel and I knew there was another 2 miles down the road. Well, the left lane was closed ahead and I got stuck sitting in traffic. I could see the gas station as the engine started to sputter. I got another 100 yards before she died.
So, I pushed the bike up the sidewalk towards the gas station only to see that it was closed and the nearest was 2 miles behind me
Luckily, I was across the street from the dealership that I bought my scooter from so I locked it up, walked across the street and they were kind enough to walk a can of gas out to me!
I would say, to be comfortable, when the last fuel bar starts flashing, pull over and get gas!