How do you reward generosity during early startup stage

Here is an ask:

How do you reward generosity during early, seed stage of the startup when you are still in heated battle?

For example - I know a sales rep (in an established startup) who sends out a gift pack (socks) to clients/referrals when a deal is closed.

As a seed stage startup where we are conserving cash, What are some of the ingenious, cost effective ideas of rewarding early customers, referrers and other helpful people.

What do people do? Just send a greeting card?