Mokonuts
Without fail, the one spot I will always go for lunch in paris is Mokonuts. The food, the owners and beautiful vibe make it so special. Order everything that is on the (seasonal and tiny) menu including the desserts. They are famous for their cookies. I love it here and recommend it to anyone asking where to go in Paris. * Reservation necessary, a month in advance via their website
Pontochoux
Cute Japanese curry spot in the Marais. Easy, fun and smack dab in the middle of all the spots so an obvious choice when you get hungry.
Mamiche
My fave bakery - it is also down the street from where we normally stay in the 9th (highly recommend staying around the 9th because you are in the middle and can get to any other neighborhood pretty easily). Anyway, back to Mamiche - everything is good here, pastries, sandwiches, cookies. There will be a line, be patient and wait because it is worth it.
Dreamin Man
Coffee, matcha with pastries such as scones or banana bread. They have 3 locations in Paris : original in the 11th, small window in the Broken Arm, in 3rd are, and now in the 1st. Always hit one or all three.