One of the things I love about bento lunches is the box encourages me to eat fruit and vegetables I might otherwise skip. I'm fanatical about vegetables for dinner, but have had a harder time adding them to lunch. And fruit has always been a snack to me, not a meal component. Bento helps me with both of those issues.
I see a lot of bento makers add apples, banana, and oranges to bento. While those are commonly found in our home, I don't particularly like them in my bento. I like to buy 1-2 'special' kinds of fruit for the Bento. Something we don't eat constantly that is more of a treat. Our treat fruit includes: mango, strawberries, raspberries, blackberries (we don't BUY those lol) pineapple, grapes (if not in season) clementines, blueberries, and cherries. Because we're also a frugal family I pick the fruit by what is on sale. Last week I was able to get raspberries buy 1 get 1 free. Those have been in my lunch all week. The week before it was strawberries. Buying 1-2 special (depending on dh's current food loves, right now its not berries) kinds of fruit keeps our bentos interesting and different without breaking the bank. Plus that is about all we can use up before they go bad! And wasting food is never frugal.