I've encountered several riders over the last few weeks who had flatted and either 1) did not have a flat kit, 2) had a flat kit but had used their tube and/or CO2 previously, or, 3) had everything they needed but didn't know quite how to execute the repair.
I'll address the situations in order with yet more unsolicited advice:
1) With cycling events and the long rides of summer upon us, no road rider should be without a flat repair kit. That's true even if you're just cruising the trail, but vital if you're going to head out on the road. Somebody will inevitably stop to help you, and it's really appreciated if have your own stuff and you can use the opportunity to learn from your good Samaritan.
I stopped to repair a flat for a couple of women a week or two ago. They had apparently been equipped with a tube and a CO2 between them, which they had used the day before.If you have never had a flat, it's easy to be confident with minimal gear. I gave them a tube and used one of my CO2s to get them going. I also suggested that when they visited their local bike shop to restock their kit that they buy at least two of everything.