>messenger bags/Laptop bags for food
Don't do it, they will cut into your shoulders over longer periods of time and give you inflamed muscles and shoulder/neck pain.
Used them during my late school days to carry my books and food, all in all less than 5kg and they fucked up my shoulder/neck area good for a long time until I made the connection.
And it wasn't a cheap bag, but a really good one with a nice wide padded shoulder strap.