Nepal  customs’ main concern will be on export of drugs and antiques as we have been  victimized of  international art theft over last few decades. All your baggeses is X-rayed on yor arrival and departure.  If officers find  any souvenirs that looks like antique, they might ask you to show certificate obtained from the Department of Archaeology. Clearing that its not antique. These controls also apply to the export of precious and semiprecious stones. Besides that , You may not import Nepali rupees. There are no other restrictions on bringing in either cash or travellers cheques, but the amount taken out at departure should not exceed the amount brought in. Moreover, Officially you should declare cash or travellers cheques in excess of US$2000, or the equivalent, but no one seems to bother with this, and it is laxly enforced.