Overall

• Trisuit (my favorite ones: Z3r0d Racer and Zoot's Ultra Tri P1)
• Sport socks
• Smartwatch (charged!)
• Gels
• A transponder, worn at the ankle
• A belt to carry gels and display the bib number
• A waterproof HRM chest strap

To read: A few tips for setting up a garmin watch for a triathlon

For swimming

• Swimming cap
• Swimming goggles
• Wetsuit (optional)

For the transition swim -> bike

• A small towel, to dry your feet and remove the dust/dirt

For cycling

• Race bike (make it lightweight! remove unnecessary equipment)
• Bike computer (optional)
• Helmet
• Glasses
• Bike shoes
• Water bottles

For running

• Running shoes
• A cap (optional)