Chess is not about traps. Only time a trap is worth knowing is if it is featured in a main line.
Playing an inferior move just to try some one trick pony and if he does not play it, your position is worse than it would be if you played normal, is something only a noob would do.
Therefore, no trap is advisable here. Instead, there are a number of sound responses, like 1...d5, 1...e5, 1...Nf6.
If you want to keep things as simple as possible, think about what you do against either the Reti (1.Nf3 d5 2.c4) or English with 1.Nf3 (1.Nf3 c5 2.c4 or 1.Nf3 Nf6 2.c4) and what you do against the Kings Indian Attack with 1.Nf3 (1.Nf3/2.g3/3.Bg2/4.O-O/5.d3/6.Nbd2/7.Re1/8.e4 - move order may vary).
Reason I say this is more often than not, it will transpose to one of these openings.
A trick or trap that can be played by black when white plays 1. G3?
If you dont know of one then just a good opening to respond with