If you are hiring a bike you need to bring the following for familiarity and comfort:
Cycling shoes
Pedals
Saddle
Helmet
Your bike measurements from home
Cycling Clothes
Bib shorts (as many as possible or hand wash overnight)
Bib tights
Short sleeve cycling jerseys
Long sleeve cycling jerseys
Arm warmers
Leg Warmers
Gilet
Cycling jacket/soft shell with rear pockets
Packable rain jacket (even in the sun an Alpine descent can be cold)
Socks
Gloves – short
Gloves – long
Bandana/cap/Buff as per your preference
Nutrition
If you know that a certain brand works for you then pack it!
Gels
Bars
Energy drink powder/tablets
Recovery drink powder