Nf6 Scandinavian and the Danish/Goring/Scotch Gambit trinity come to mind. Do like your comment on the KID ... a lot of white players at the club level really do struggle against it.
Average Time controls used in this club also matter. For less than 30 mins, Almost any gambit is extremely effective as you are counting on presenting your opponent very analytical + sharp positions for him to calculate OFTEN during the game (but you have seen before via preparation).
So it is a question of dragging him to your backyard instead of you getting dragged into his ... where your backyard is filled with beartraps, landmines and Lady Gaga playlists .... these require delicate steps by your opponent to avoid.
Additionally, "delicate" stepping + burning time on his clock means a lot more when you don't have enough time to begin with.
Defining club as <2100 what 3 openings do you believe to be the deadliest weapons at club (ignoring 'depends on players style' stuff).
The top ones that come to mind for me:
Benko Gambit (having played against it OTB, it isnt pleasant for people <1900).
Trompowsky Attack(my experience from playing it, many players commit positional suicide in many lines, not understanding the subtleties).
Kings Indian Defence (Having struggled against it OTB, even against weaker players who seem to have some very automatic plans (at least against my lines) made it a very tough nut to crack).
I would also give special mention to some openings such as the Sveshnikov, which I have had astounding success with OTB as well as the Blackmar-Diemer which is very useful at lower level CC chess (and probably <2000 OTB) if youre familiar with the theory.