There are lots of coin lockers at the airport or for if your bags are really big or a lot there is a service counter to store luggage. You can store the luggage at the airport and then go into the city without having to lug it. HND is very close to Tokyo. You can be in Tokyo within 30 minutes. I would say you might have about 3 hours for your layover depending on your level of comfort. You can store at the train station as well for when you do the transfer from NRT-HND.