You don’t need to bring anything special with you, just what you would normally bring for a stay in a hotel in Nepal.
There is a range of possibilities for trekking and hiking and if you wish to go for walks then bring some comfortable shoes. In monsoon months (June, July, August) beware of trails that become slippery. So bring good walking shoes
Winter nights can be cold so prepare perhaps with a hat, gloves and some warm clothings. Much of this can be bought at very reasonable prices in the famed Thamel market in Kathmandu.