Spelunking is a good activity for adventurous type who wants to get their hands dirty and who are not afraid of dark and tight spaces.
What to wear:
1) Clothing. The usual clothes to wear would be shorts, jogging pants, and leggings and a shirt. A rushguard is also convenient as it dries easily. The rule is to wear lighter clothes as possible. You will be soaking wet inside the cave so it would be convenient to wear light and easy to dry clothes as possible. I love leggings more because it hugs your legs and is very good in silhouette photos. =)
2) Gloves. To protect your hands from the scrapes and dirt. As much as possible, wear gloves that has a very good grip. If you're not bothered to get your hands dirty, it is optional. I still think, spelunking with bare hands is the most effective.
3) Shoes and Slippers. The rule with shoes and slippers is to protect your feet but make sure that it won't cause you to slip as you would be walking in uneven ground. As much as possible, where shoes that has a good friction. Also, where footwear that you don't care much when it gets dirty and wet. You may walk through puddles, mud and sometimes get your whole body soaked.
During my Sagada experience, I didn't wear much of my slippers because it causes me to slip.
What to bring:
4) Headlamps and Flashlights. This is optional since most of the guides have a lamp to light your path. But it is convenient to have headlamps to see your next step. Sometimes bringing flashlights is a hassle because you would need both of your hands to climb rocks or grip when sliding down.
5) Cameras. It is alright to bring cameras with you to capture the experience and the great moments during your spelunking trip. But as I've mentioned in #4, you would need both of your hands, you won't take as much pictures... and when your hands are dirty, you won't try to hold your cameras anymore. So arrange with your guides that they would be the ones to take your pictures so that you would still have every moment in print.
6) Water. Bring ENOUGH water. Don't bring the whole 1L bottle. It's too heavy! Just bring enough that you could sip through when you feel thirsty. It's a long activity and you need to re-hydrate. Again, some guides would allow that they would carry your things but if not, bring enough so that you won't have a hard time.