I have made some happy customers in my line of work for simply giving them the small part they need.

Most places have minimums basically to cover the costs associated with printing an invoice. We have some strict accounting policies and audits that look at our less than $50 sales. It was stated that every ticket cost anywhere between $90-140 just to print the ticket, bill the customer and wait for payment.
We have a $50 minimum, but if a guy needs something under about $15, I just hand it to him and have the boss adjust it out of inventory. This has been great PR as some guys have come back to order much larger orders and asked to have the 'free' part I gave them added to it, as they really appreciate helping them in a time of need.
Some guys have just thrown some cash on the counter and said, "Here is a tip for you to by the guys some sodas".
I can't believe how some places operate.
Randy