I don't think it's really accurate to think of it as an arms fair - although certainly there will be weapons on display.
Farnborough is about two things: aerospace and money. That the show was originally organised by the "Society of British Aircraft Constructors" tells you a lot about that, although it's a lot of years since things had to be British to be on display at the SBAC (now Society of British Aerospace Companies) show.
Clearly both flying machines, and things for shooting either at or from them, fall into that double category. But, you'll find in the trade exhibition a massive range of "stuff" that also does that: flying clothing, jet engines, rivets, crashproof seats, hangars, insurance, avionics - absolutely anything you can think of, and much you can't. The only really common factor is that the more expensive things are, the more likely they are to be at Farnborough. There's not a lot of room for cheap aviation, and not many opportunities to buy things and take them home with you. There will be massive numbers of opportunities however to take home brochures about things you will never be able to afford.
G