There are not many things that you can buy in Rewalsar that are impossible to find elsewhere, but if you have been looking for certain things and they sell them at the monastery stores, it is nice to support the monasteries and buy here. They generally have good quality items at reasonable prices, so there is no need to bargain, as everything is at a fixed price. Emaho cafe a nice selection of incense, oils, soaps, and notebooks, as well as some traditional Tibetan clothing that is well-made of good quality cotton.
The Nyingma Gompa sells blessed colored strings, a nice gift for a group of friends or colleagues, and the juniper incense that is used in the big smoky incense burners that they use to “cleanse” the temples and other buildings. It is a very traditional formulation, and while it may be available in other places, it is only Rs 30 for a small bag if you wanted to try it yourself.
The shops in the Tibetan side of town – just past Mandarava's cave, sell a selection of decent quality Tibetan items - anything from bells and dorjes, singing bowls, clothing, kataks and other Tibetan trinkets. A couple of shops sell Kullu shawls and scarves.
Just past the Tibetan block of shops you enter the Hindu Temple area. If you are looking for a good book to read try the Guru's Feet Coffee Shop next to the Shiva Temple, they have a nice selection and you can pick up some Indian handicrafts and gifts there as well.