Weeeeell, there are five common ways that folks show affection to one another: Words of affirmation, quality time, physical touch, acts of service, and receiving gifts.

We all do some combination of the five, but our specialties lie in one to perhaps three of them. Never think any less then all of them is invalid. Instead, consider the things you like to do to show another person that you care and embrace it. I myself confess that I don't receive gifts well. But I'm happy to use my skill to keep them well-fed and speak from my heart. I'm also fairly touchy-feely.

Now, you... I don't think you'd jump into something quite so complex as this for someone you bumped into on the street.