You can see so many things around. Go to Rohtang pass that has a freshwater spring, Visit the mall road and shop all you want, drink a coffee at the cafe of your choice and indulge in the beauty of this valley.
If you are lucky you can do Zorbing and Paragliding at Solang Valley. Manikaran is a beautiful Sikh Temple with the natural hot sulphur spring and one should not miss it.
Kasol is not too far from Manali and you can definitely give a day to Kasol while planning to come to Manali. The theme cafes and the laid back attitude of the place gives you all you need.