It is good to know about the trick with the inventory, I'll be sure to use that now. I think some of mine weren't eating their lunches because of that.
The sack lunch does have a few uses. It gives a moodlet if someone wants it. (If someone is going for a promotion, maybe that will help to nudge them into a better mood). I find it to be pretty useful for the GTW careers because it is an alternative to buying from the vending machine. It's a way for a sim to save a bit of money by remembering to bring a lunch. My doctor/detective sims don't always bring a lunch but most of the time, they do now. You can also turn leftovers into a sack lunch as well which is also cost-effective and uses up leftovers. You have to think a little bit about the freshness of the food because older leftovers won't keep as long during the day in an inventory.
I think it's just another option. I know some people don't care about the food at all. In my case, it keeps things a bit varied.
