Lived here long enough to try everything multiple times, here's the honest breakdown:

7-Eleven: best karaage (¥150), solid onigiri selection. Premium sandwiches are overpriced at ¥300+ but genuinely tasty 🍗

Lawson: dessert champion. Uchi cafe sweets are addictive ¥150-250. Their karaage is also solid competition 🍰

FamilyMart: best coffee by far, surprisingly good pasta. Famichiki is overhyped but spaghetti carbonara ¥298 is legit ☕

avoid: any konbini sushi when you're literally blocks from Tsukiji outer market. Fancy bento over ¥500 are tourist traps when teishoku exists

freshness timing: hot food turnover peaks 12-2pm and 6-8pm in Shinjuku/Shibuya. Thats when everything just came out