Figure out your few signature items and really push those.
I see deli kind of retailers lean into custom everything to their detriment. Espeically in a place not known for good delis, you need to educate your customers on what a good deli sandwich is.
This will also DRAMATICALLY speed up your speed of service. If you have a few sandwiches in mind, you can pre-measure out your meats, things like tapanade or sturdy veggies and just assemble and add any moist ingredients necessary at the last moment.
Start small, then lean into events. Catering is where the money is.
A plant shop near me does potting nights where you just go, pot your plants and get free soil with a new pot or plant purchase.