Your lunch needs a dry bag, not a lunch box.
If you ride a bike or motorcycle to work, the best lunch bag is a roll-top dry bag with a hard container inside. A regular lunch box gets crushed, leaks, or doesn't fit your backpack.
The problem with most "lunch boxes" is that they're either flimsy soft coolers or rigid clamshells that waste space. Neither handles rain, vibration, or being jammed into a half-full backpack. A roll-top dry bag solves all three: it's fully waterproof, collapses to whatever shape you need, and any rain that hits it rolls right off. It's the same thing kayakers use to keep gear dry, so durability is basically a non-issue.
The catch is that a dry bag alone won't protect your sandwich from getting squashed under your u-lock. So put your food in a cheap rigid container first — a Sistema or a glasslock works fine. That combo beats any insulated lunch box on the market for actual commuting.
If you really want brand names, Sea to Summit makes the best roll-top dry bags for this (their Ultra-Sil series is light), and Earth Pak is the budget option. The Yeti lunch bag is nice, but it's a waterproof-ish soft cooler, not a dry bag, and costs way more for the same protection. For the truly paranoid, a Pelican case is indestructible but too heavy and bulky for a backpack.
Don't buy a cute bento box. Buy a dry bag and a cheap container. Future You won't be eating a soggy, crushed sandwich in the rain.
