When you hit level 70, get the Scotty Cameron Phantom X putter. Made a definitive improvement in my scores when I bought it and wish I'd done it sooner.
The L59 Ping irons are a good buy and a bit less expensive than the higher level alternatives. High trajectory means less roll on the greens.
Wait until L74 for the Taylor Made driver. If you're out of credits and need to wait, get one of the Callaway drivers in the mid 80s.
The Vokey wedges unlock in the late L70s and are better than anything available before them. If you only buy one, get the 64 degree wedge at L80.