I've never been one to carry lots of crap around in my bag. But I do try to pack for any situation in a light manner. My backpack is a canvas rucksack picked up at a night market in Taiwan. What's in my bag:

• iPad 3 with Bamboo stylus - great tools to have for students
• Brave New World by Aldous Huxley, currently reading for class but I really enjoy it.
• Water bottle - old VOSS bottle that I scratched the label off
• Pencil case - case from Taiwan
• Calculator (TI-84 Plus)
• Wallet - from a street vendor in Taiwan. This bad boy has lasted me two years with not a single issue. 
• Cell phone - Motorola Moto G with Eagle Cell case
• Apple earphones
• Domo bag with tampons (hey, don't judge)
• Lancôme makeup bag
• Mirror
• Elizabeth Arden Exceptional Lipstick in Breathless (discontinued)
• Boots Botanics Tinted Lip Balm in Sheer Pomegrante
• Bath and Body Works Fresh Picked Passionfruit Lip Butter
• Folding hairbrush
• Bath and Body Works Japanese Cherry Blossom Hand Sanitizer
• True Religion Love Hope Denim Perfume