The classic James Bond gun, the Walther PPK is one of James Bond's many trademarks, as you can easily associate the two. The Walther was introduced in Dr No as a replacement for the Beretta he had before. M assures 007 that it has a "delivery like a brick trough a plate glass window".
This gun was used in most of the other Bond missions as well as Dr No.
This rather chunky, bulky looking gadget was actually a Geiger counter. 007 uses it to scan inside Quarrels boat where he finds some radioactive rock samples. This might not really be seen as a gadget since it is so big and obvious.