Instead of focusing on the main character in this prompt, write what the secondary one says in reply. Why is the teenaged employee the only one at the registers? Is everyone else out sick? Was there an avalanche that prevented everyone but him from coming into work? Use your imagination!
She stood in line, glancing out the store's front window as she transferred the grocery basket back to her other arm. What was taking the cashier so long? It wasn't like this was rocket science! She had more important places to be, and she should have been there ten minutes ago. Sighing in exasperation as she finally reached the front of the line, she looked around at the other cash register stations while she unloaded her canned soups and yogurt.
In that one quick glance, she realized why the line had moved so ridiculously slowly. "So...you're the only one here, huh?" she asked the frazzled teenaged cashier.