Another wedding photographer here.
I don't expect a meal to be provided but I do make it clear that, if I don't get a meal, I'll be going off site for 60-90 minutes in search of an adequate meal - hot food.
Taking a lunchbox isn't possible. I don't have anywhere to store a lunchbox other than my car and, considering the majority of my weddings are during summer, the only thing's I'd be able to eat would be something that doesn't melt, something that doesn't need to stay chilled and something that doesn't go off.
Now, would I want to eat a lunchbox full of snacks? No. During a typical wedding day, I'll drive 2-3 hours to get to a wedding, start shooting at 10am and then finish at 9pm. I won't stop walking from the second I start until the minute I finish (to drive the 2-3 hours home) apart from about 45 minutes during the wedding breakfast. My steps range from 25000-30000 steps per wedding day. Will I manage on just cereal bars and crisps from a lunchbox? No. I need a substantial hot meal.
I ask my couples before the wedding whether or not they are providing me with a hot meal and, after explaining the above, I've always been supplied with one. They don't want me to leave the venue in case I miss anything.
Actually, one time, I was told I was getting a hot meal but was given two slices of bread and some chicken (a chicken sandwich). After such a long, physical day - having not eaten since my breakfast - I was ill. I felt sick, was shaking, had a headache, thought I was going to pass out and was so hungry I couldn't eat. I was so ill I had to cancel a job the next day and lost £800.
So, us photographers ask for a hot meal because a lunchbox of snacks is inadequate and I don't want to miss anything while I go off site in search of hot food. It's as simple as that.