Split the bill
Nobody carries cash anymore except bartenders, strippers, and grandparents, so paying with multiple cards shouldn't come as a big surprise. Bonus points if the server brings out multiple pens for signing all those merchant copies.
Effortlessly transfer tabs from the bar to your table
The world of POS systems is a rabbit hole that no man should ever have to go too deep into, but it seems likely that if someone's drinking at a restaurant bar, they might be waiting on their table. When a bartender's able to magically transfer it to your server, it makes you feel like they're anticipating your every move.
Have individual unisex bathrooms
All the girls waiting in the line for the bathroom isn't just a lyric from an old Pharrell song. Often, there's a serious gender inequality in bathroom waits, and having individual bathrooms that swing both ways helps relieve everyone way more efficiently.
Direct you to those unisex bathrooms without prompting Everyone's been there: squirming aimlessly around the restaurant and poking your head into the kitchen and employees-only areas. It's always wonderful when, instead of just letting you wander around like a headless chicken with a dangerously full bladder, a server simply points you in the right direction.
Stock bathrooms with fancy soaps and nice dryers Sure, a squirt of that pink ooze will destroy any bacteria that might be lingering, but it smells like a science lab and makes your hands feel rough as a stray cat's paws. A small investment in nice soap let's the customer know the restaurant cares. Bonus points for hand dryers that actually work well, or paper towels that aren't in a big soggy stack.