Some of the things I miss, in no particular order:
Chilling with my friends, drinking any random microbrew, distinctive...or just plain cheap beer we happened upon.
Fluffy, spicy percolated clouds and the good company. Some cozy, some cute, all enjoyable.
Pizza nights! Taco nights! Any excuse to gather, grub, and socialize was fun. Not that we don't do that here, but my jokes don't go over as well.
People getting my sarcasm...the easy comfort of joking with old friends, nothing lost in translation.
Good beer and the huge varieties readily available at a wide array of locations and all so cheap compared to Japan! Beer is sold by the can/bottle here and is usually about $2US for one, large, can. No 40s in sight. I don't miss 40s, but buying a 6-pack of bottles for $8US sure was nice.
Mexican food, south American food!! Dried chiles, carnitas, arepas, birria (stewed goat), queso fresco, crema, salsa verde, negra modelo, cilantro, freshly fried tortilla chips, frijoles negros...cheap and widely available back home. One night at Mexican restaurant in Ebisu was about $50US! Making tacos at home was still about $20US. Que lastima!!
Spanish. Yo hablo poquito Espanol. Spanish, to the Japanese, is probably on par with speaking Japanese back home... You certainly could, but the chances to use it are exceptionally rare and locals might look at you with puzzled wonder.
Not being asked if I have a boyfriend ALL the time...often by total strangers. At least back home that was usually reserved for awkward guys trying to pick me up, not random girls i'm drawing, strange old men in a restaurant, etc.
Long drives through the desert...the landscape...listening to music with the windows down...my old car.
The peach tree from the house I lived in during highschool, with the fluffy bright pink blossoms that would explode every spring. Lush green, private, yard with a leafy tree providing shade. The BBQs, fire pits, the laughing of old friends or lounging in the sun reading in a bikini.
American produce...while I honestly adore a lot of Japanese produce, there are some things I just can't find here... butternut, acorn or spaghetti squash, for one. Kale. Fresh non-asian chiles (jalapeño, Serrano, etc)...broccolini...Swiss chard. Fennel. Pumpkin.
Pumpkin spice everything. Pumpkin spice lattes are one of my greatest joys in the fall/winter.
Eggnog...and spending the winter solstice with fiends and family...
Bonfires in the desert. Off-roading. Horseback riding.
Cultural diversity...walking into a store full of people speaking Korean, another where everyone speaks Tagalog, one where everyone speaks Spanish...
So on and so forth. So it goes.