Day trip to Yokohama? Recommendations?
Definitely go to the Yokohama Ramen Museum. FIrst stop inside should be #1 stall, Ryusyanhai and the second stop #6 stall, Komurasaki. After that choose a third place, maybe #2 Ganjya or #7 Sumire. That should be your last stop. Whichever looks best to you.
If you don't mind getting off the beaten path and are adventurous, then I highly recommend visiting Taya Cave with its elaborate rock carvings. Although they give you a candle to explore, bring a mini flashlight just in case. You have to take a train to Ofuna station and then a short taxi or bus ride to get there. To get back to the train station is about a 30 minute walk or bus.
Chinatown is definitely worth it. Yokohama's Chinatown is very clean and a sensory overload of food after food. It's just very different from Chinatowns in NYC, SF or Vancouver. It's a lot cleaner, more touristy (but in a nice way), more food-oriented. It's fun to go in the evening. Actually, it's nice to go hang out late afternoon at the nearby Yamashita Park, then go roam Chinatown into the evening. It's really happening there at night, especially on weekends. Although many foreigners crap on Japanese-style Chinese food, I love it. Well, it's the stuff I grew up on. And there are certain Chinese items that Japanese do very well with, and those include ankake (pan-fried noodles with ankake), XLB's, fried rice (chaahan), maobo tofu, spring rolls, ebi-chili (shrimp in sweet chili sauce) and mango pudding. You get some pretty damn good shumai in Yokohama... actually prefer Japanese shumai to Cantonese ones.
Ramen museum should be on your list if you love ramen. Keep in mind that Chukagai station (Chinatown) to Shin-Yokohama (Ramen Museum) is 20min by train, and Chukagai to Shibuya is only like 30min. So, even if you're based in Tokyo, it's not like you have to do all the Yokohama things on one same day.
I love the Minatomirai area, as well. But I've never been to Kirin beer garden.