You need at least two pairs of skis, one for SL and one for GS...and more if you're going to do speed events. There's tons of discussions in this forum and elsewhere, re brands, lengths, sidecuts, and so forth, so I'm not going to repeat them here, just do searches.
However, in addition, you'll need:
- SL armor. Shinguards, pole guards, a SL top, a SL helmet with chinguard. You can get a helmet for GS and take the chinguard on and off, but I prefer to have a dedicated SL helmet.
- Probably a GS suit, or a DH suit with something like a Spyder Stealth top. Aero is worth 4 to 6% in a 60 second run, and you can't afford to give that kind of margin away in a Masters race.
- Check your boots. If they're not an honest to God race boot, consider getting one.
- Tuning gear and wax. If you don't structure and wax, you'll get beat by people who do wax but don't ski as well as you do.
- Hit the gym, ride a bike, play tennis, go hiking...do whatever you have to do to improve your strength, flexibility, quickness, agility over the summer. Skis matter; the pilot matters more...
- Watch some WC video, as in the 2008-2009 WC Winning Runs DVDs. Also the USSA Skills 1 and 2 DVDs.
There, that should get you started...