Sandwich was the name Peter Parker gave to a stray dog he found on the streets while patrolling the city as Spider-Man. He gained its trust by giving it a sandwich he found in a dumpster, hence the dog's name.
Peter tried to keep Sandwich hidden at his Aunt May's house. However, she quickly found out about Sandwich and called animal control, arguing they couldn't keep a dog, much to Peter's disgruntlement. The dog was eventually taken away.