Employees and stations that allow you to manufacture on a single store scale far earlier than factory manufacturing, to give you a few more options and make fast food a little meaningfully different.
Food would be the big one, to differentiate fast food from restaurants, you could either deliver already prepared, or deliver ingredients and cook on site.
But you could also expand to other simple goods, like cheap gifts or small scale craft beers perhaps.
This would be another lever to let you optimise businesses, but also give you another way to actively work for the business when you have a spare moment, even once you have employees. Give the player the cook and craftsman skills, and you could go pump out a batch of mugs or whatever to save some cash. Selling your own crappy art is peak small business.