I believe human interaction is important. I also believe that entry level jobs are important, whether they are held by teenagers part-time or adults working to support themselves and/or their family.
As such, I avoid self-checkout aisles, and at the gas station I don't pay with a credit card at the pump whenever possible. I pay (even via credit card) through an actual person--an employee. I don't direct deposit or use an ATM card--I go to a teller at the bank.
Employers watch and pay attention. If a worker doesn't serve customers, they are not longer needed. If the employer deems a position as "no longer needed," the job disappears. Individuals that hold that "no longer needed" position are out of job.
Sure, they could get additional training and get a better job--one that pays better and has benefits, etc., but they are either working entry level jobs (such as a cashier), or jobs that could be eliminated if faceless automation takes over (such as with a bank teller). Even more, I am polite and strive to greet the individual with a kind word or comment. Just because the job doesn't pay well doesn't mean it is fun and stress free.
Yep, call me old fashioned. It takes a little more time and effort, but I think it's the right thing to do.