Tucked away on a second-floor shelf of Gene’s Sausage Shop & Delicatessen is a library of gourmet mustards that will forever change your lunch life. Be forewarned: Given all the temptations on the ground floor, many visitors never make it upstairs. Gene’s owners, the Luszcz family, have been making gourmet sausages in the city since 1972 and Gene’s has ’em all, piled as high as a pitmaster’s cords of firewood: plump garlicky Knackwursts, parsley-studded weisswurst, kielbasas, Alpine sausages, Hungarian snack links. Grab some, then head up to Gene’s mustard cabinet, which is stocked like a Bavarian beer hall with tasty curios, like boutique domestic spreads and toothpaste-shaped tubes of Develey mustard, guaranteed to become your picnic basket’s new best friends. 4750 N. Lincoln Ave., Lincoln Square