I found this a couple of months ago. It's from back when I was in college, and a bunch of us drove up to Tennessee to go spelunking. It's... well, it's old enough to be printed on dot matrix. And if we're being completely honest, it was a very old-fashioned approach to caving even then: three people, two lights per (at least), and old clothes. The complete lack of helmets and any other safety equipment tends to freak out more modern spelunkers.
So this is what I told people to bring. My commentary is in italics.
Things YOU should have with you when you go caving:
1. A pair of heavy pants: jeans, army surplus, something solid and DURABLE and expendable
2. A T-shirt and shorts: These can be worn under your caving clothes, or you can change into them when you get out of the cave.
3. A sweater of sweatshirt: Preferable old and expendable, but it needs to be something Warm. Caves maintain a year-round temperature of fifty-four degrees, and when your feet get wet, you'll get cold very quickly.
4. Thick socks: They won't actually help keep you warm, but they'll help when you get pebbles in your shoes (more padding).
5. A pair of lace-up, ankle-length shoes: Hiking boots, high-tops, or possibly combat bots. Do NOT use low sided tennis shoes as they tend to come off; do NOT use cowboy boots either, once you get water in them you'll never get it out.
6. A tough jacket: Jeans jacket, army surplus; something you can afford to get dirty, something fairly tough and tear-resistant. Leather is Not recommended, as it is fairly heavy and tends to get heavier when it's wet. This should be something loose enough that you can wear it over a sweater or sweatshirt and still move in it when it gets wet.
7. (optional): While a pair of gloves is next to useless, you might find that a pair of old mittens will help keep your fingers warm when you're not climbing anything or crawling through water or wriggling through small holes.
8. A flashlight: This is VITAL.
9. Extra batteries for the flashlight: This is also VITAL.
10. Also in the VITAL category: one OTHER source of light: a cigarette lighter and candles in a ziplock bag, a second flashlight, a glow-stick... Something.
11. (optional) A hat, bandana, or other object for protecting your hair and keeping it out of your way. If you're worried about hitting your head, helmets should be available.
12. (optional but recommended, not vital) Knee and elbow pads.
So there you have it. That was quite a trip, actually, and I might have to tell some stories from it. For that matter, I have some fairly humorous caving stories too. Hm...