You can read more about some of the additional expenses you will incur on your Everest Trek.
There are a few items on the trail that you will need and want to have some extra money for.  More and more, you are able to visit cafes, have clothes washed or purchase snacks or souvenirs on the trail.  You can generally purchase and use WIFI throughout the entire trek, in each village.  At the end of your trek, you will want to tip the guides/staff in Lukla for the wonderful work they have done!  So you definitely want to have some spare money with you on the trip and the amount will depend on how much you plan on buying!  You can read more about some of the additional expenses you will incur on your Everest Trek.