If you like hot spring,you should go to atami.
It takes about 2hours by bus from Tokyo. You can enjoy Mt.fuji sightseeing, sailing at ashinoko. You can see some musiums and seel inspirations.
It depends on what you want to do and see. You can pick the bus or train for the transportation, then will be able to visit so many places on 1day! If you are in Japan now, then you can take a train to the north for skiing, or take a bus to Mt. Fuji & Shizuoka area for Sakura! Or to the Nikko and Onsen by train! There are too many places you can go on a day trip. You better find what you want to do or see, then find the best day trip you want to! Have a wonderful day trip!