I've never used the electronic gadgets myself. There are 2 that I know of.

The company that makes the Firebird line of planes has something they call the Sonic Combat Module that plugs in to some of their airplanes. The airplanes are low-performance electrics, but from what I hear, they are a lot of fun.

The other device is a bit more expensive, but designed to work with any RC setup. I don't have the contact info for it, but I know there was at least one thread about it on here (or, maybe, the RCCA forums at RCCombat.com, I forget). Anyway, it looked neat, but I've no idea how it worked, and it was a bit expensive.

Bomb drops and such aren't part of combat competitions. That's more a fun-fly thing, so this is the wrong forum for that.