A sandwich is a popular lunch item that is usually comprised of meat, cheese, vegetables, bread etc. When Harry Potter first met Ron Weasley on the train, his mother prepared him four corned beef sandwiches for the journey, despite the fact that he was known to hate them. Ron Weasley's comfort food was his mum's bacon sandwiches.
In 1992, when Harry and Ron showed up late in the Flying Ford Anglia, Professor McGonagall produced a plate of chicken and ham sandwiches for them to eat in Snape's office so that they didn't disrupt the Welcoming Feast. Also, after Harry Potter's defeat of Lord Voldemort, he wanted nothing more than to relax in his four-poster bed in the Gryffindor dormitory and have Kreacher bring him a sandwich.