1. A FULL WETSUIT: "Full" meaning complete coverage of your torso, arms, and legs. A more buoyant suit—like 2XU's Team 0 Suit—will save you energy in the water ($249; 2xu.com). If this will be your only tri, a surfing suit will do (but expect a less comfortable swim), or look into Xterra's rental program (from $39; xterrawetsuits.com).
2. LAYERED SWIM CAPS: Two caps is the standard for keeping your head warm in the Bay, but you'll get just one in your goodie bag—made of latex or silicone—and you're required to wear it. Bring two extras—one latex, like Tyr's Latex Swim Cap, and one silicone, like the company's Wrinkle-Free Silicone Cap ($3 and $10; tyr.com)—so you can wear a second without mixing materials: Latex and silicone slip off each other.
3. TRI SHORTS OR RACE SUIT: Having to change from wetsuit to biking shorts, then biking shorts to running shorts, will cost you time. Instead, start the race with Pearl Izumi's Tri Shorts ($55; pearlizumi.com) or Zoot Sports' Tri Racesuit ($100; zootsports.com) under your wetsuit. Both are quick-drying and provide a chamois for cycling as well as a chafe-free design for running.